One of the great western national parks, like Yellowstone, would be wonderful for a few days if you are able to work it in. It's a gorgeous & unique natural landscape you don't see elsewhere.

DC is always nice. Lots of free monuments & museums. There's the C&O canal, Georgetown & Alexandria waterfront; the Zoo, Great Falls, etc. Tons of free or inexpensive, yet interesting, things to do with kids! There's also three pretty nifty amusement parks with in a decent car rental drive from DC.

The rest of our country, except maybe Ohio, is also wonderful to see! We have national parks and, um, national parks.

Since you're going in August, you might find the Southeast a bit hot & humid, unless you're into that sort of thing. The Northeast has some wonderful coastal sightseeing. Where ever you go, try some local food!

Just kidding about Ohio, or am I?

amy_f beat me to it, but i definitely suggest yellowstone or grand teton or any of the "quintessential" national parks. the bigger parks in the west have so much wildlife to enjoy (especially for small kids!) not to mention spectacular landscapes and a tourist infrastructure that makes traveling with kids a breeze. it's hard to beat! and the weather in august can be perfect-- comfortably warm during the day and cool at night. go west!

Definitely not Disney World in August! HOT.

Maine is wonderful in August. I am from the Southeast and I dream of going there every summer since my husband and I honeymooned there. Acadia National Park is there and it is amazing.

Northern California: Big Sur, Point Reyes, Mendocino (and San Francisco along the way).

I would love to suggest you rent an RV and do some visits to some of the big parks, especially Mesa Verde and the Great Sand Dunes - we actually did this this August as our family vacation. In Mesa Verde, I'd suggest the KOA in Cortez - if you aren't RVing it, you can get a cabin there, and either cook your own food over the fire or eat at restaurants in Cortez. You can do Mesa Verde with two full days in the park - spend one on each Mesa. Head into the park early the first day and pick up tickets to the guided tours (3$ a pop) and do the guided tours for each mesa as well as the self-guided - it's an inexpensive great way to see history. At the Sand Dunes, you can park your RV in the park or at the Lodge just outside the Sand Dunes, and spend a couple of days playing on the Dunes. In August it does get quite hot on the Dunes by the end of the day, but there are some great programs throughout the day and Zapata Falls is a must.

QueenOfTheFall: I disagree! Ohio is an awesome place to visit. It's beautiful, there is the Rock N Roll Hall of Fame, Cincinnati has one of the best zoos in the country, Columbus has Cosi etc.
But if I lived out of the country I would go to NYC, Niagara Falls, Yellowstone is AMAZING! Try to make it to a beach, North Carolina, California, Florida, You could go on a swamp tour. That would be fun!

Yes, I would be sure to get into the mountains. While the Berkshires or Appalacians are great, the Rockies have that wide-open immensity that is unique to North America. Denver and Boulder have perfect weather in August and would be a good home-base for a few days of exploring the mountains.
California's Sequoia National Park has the giant redwoods that are just flat gobstopping. It's fun to drive up the coast.
For cultural exchange, head to the Carolinas, Georgia, or Louisiana. You will be charmed by the southern hospitality and food, and find the history quite eye-opening. It will help you better understand America.
The Great Lakes are wonderful. Chicago has days and days worth of family-friendly activities right on the the shore of Lake Michigan, but any of the five lakes would be worthwhile visiting.
Where-ever you end up going, I'd seek out a children's museum to visit. They will have age-approiate info on the area's history, landmarks, geography, etc. And it's a nice way for your kids to meet some American friends.

Never met a Brit who didn't like the Northwest.

http://www.bbc.com/travel/feature/20100917-top-15-pacific-northwest-highlights

Also add Central Oregon to the list. Dry, sunny every day, great views and family friendly.

Yosemite. It's a must see.

Raissa, Big Sur is beautiful but it's a long, long way from pretty much anywhere, although come to think of it most of California's great parks are. It's sort-of near Hearst Castle, and Monterey, though. Monterey has a great aquarium but I don't recall much more about it.

If you want to do California state parks, it really depends on where in California you go. Yosemite is beautiful but absolutely packed in summer and it's about 4 hours East of San Francisco and maybe 6 (guessing here) from LA. I personally like Lassen National Monument better because it's not as busy and it has some really nifty geothermal stuff, especially Bumpass Hell. It's maybe 4-5 hours drive north of San Francisco and I have some really fond childhood memories of the area. Subway Cave, at the north end of the park, is a real treat and so is Spattercones Trail. If you want to get even further afield, Lava Beds National Monument is really, really cool but it's maybe 2-3 hours north-east of Lassen so that might be further than you want to go.

Near San Francisco is Muir Woods, an old-growth redwood forest. It's truely beautiful and one of my very favorite places in the Bay Area. It's got good hiking and is a nice place to escape the hubub of the city if that's what you're after. It's near Mill Valley and San Rafel, both "picturesque" towns that I have driven through but not really explored. It's also pretty close to a lovely overlook of the Golden Gate (although in August all you're likely to see is fog) and some abandoned military stuff that's a blast to run around in. Cross the GG Bridge back into SF and you'll be right above Fort Point which has tours, if I remember correctly and is also quite fun to run around in. In the city itself is the Exploratorium, a hands-on science museum (with kids, you can't miss this, it's AWESOME), and the California Acadamy of Sciences which has an aquarium and a really neat rainforest exhibit along with the more touristy attractions of Ghiradelli and Union Squares, Chinatown, Alcatraz, etc. And Angel Island, where, it turns out, you can camp overnight if you make reservations. Since it's in the middle of the bay, it gives a great view of SF and taking the ferry over is fun.

If you want Southern California, the San Diego Wild Animal Park is all kinds of awesome. It's sort of like a zoo but with no cages so the animals are roaming in somewhat realistic landscaping. You can even do a photo safari and feed the animals! (I still haven't done this and really want to). It's about a 2 hour drive south of LA. There's also Joshua Tree National Park, which I am not familiar with but friends swear is cool. In August, you should be able to catch a baseball game if you so desire but I remember finding them boring as a kid.

I wish I was more up on my "wonders of California" schpiel but oh well. Keep in mind that California is BIG and if you're driving it can take a very long time between places. It's pretty easy to be driving for five or six hours without seeing much at all so just be aware. Enjoy your trip!

Ohio is a wonderful place to visit and actually the Columbus Zoo is the Number 1 zoo in the country right now according to USA travel guide. Not to mention Cosi and The Wilds.

http://www.wrsol.com/usatravelguide/2009/02/top10zoosinamerica/

There's a lot to love on the west coast! I'd say start in northern California in the redwood forest and then drive up the coast. Lots of parks, beaches, and views. Lovely tide pooling...

It depends on what region you're going to be in. When my husband's family comes to visit here in the mid-west they really enjoy upper Michigan.

YOSEMITE!

Come to the big apple and see a show or two. And definitely go to Dillan's candy shop and FAO Schwartz Toy store (my favorite pastime) There's the hersheys chocolate factory too in PA if you want something further out. http://www.hersheys.com/discover/visit.asp

oh, and I agree with Annieglan- seeing the alligators in the swamplands of florida, south carolina, etc is really fun. Just find some park where they can get up close. It's not the same feeling as a zoo trip.

I definitely suggest leaving the coasts at some point in your visit. One of the majestic things about the United States is how vast it is and how varied its lands are, and you can't fully appreciate that from I-95 or Highway 1.

Just a suggestion from Kansas. Enjoy your visit!

New England is very nice in August. Maine for lobster and the ocean, New Hampshire for lakes, and Massachusetts for Boston activities (such as The Freedom Trail).

I forgot to add...Santa Fe, Taos, Grand Canyon, Canyon de Chelly, Bandolier National Monument, and/or Mesa Verde. The southwest and the ancient homes of America's native peoples are not to be missed!

although i am a born-and-raised Midwesterner, i would definitely NOT suggest a visit to the Midwest any time in August. unless you desire to regale your friends & family with stories about heat exhaustion and ridiculous humidity. i have visited Colorado many times during August and agree that the climate is very favorable. plus there are tons of outdoorsy things to do and the scenery of the mountains is breathtaking.
Yosemite is amazing. you can't go wrong there!
if you want a big city experience, NYC or DC would provide tons of exciting options in a relatively small area. plus a lot of things for kids to do.
it really just depends on where you exactly you end up going. there are tons of things to do/explore/learn about in this fine country. good luck to you on your travels!

Another vote for New England.. specifically Bar Harbor and Downeast Maine... which is known for it's acquired nickname, "Vacationland" It's beautiful, budget friendly, and August is one of the best times of year to visit... no worry about heat and humidity.. it will be perfect weather.. 75 F...

New England is beautiful and has lots of fabulous options and lots of history ;) I live out west and happen to think it's a fantastic place to explore--though you'll want to pack layers for bundling up. Yellowstone National Park is right in my backyard, is amazing in and of itself and offers activities, as does nearby Jackson Hole Wyoming and Big Sky Resort. My little boys LOVE it all. Wildlife, hiking, lakes, stunning scenery. Arches National Park or Zion's National Park in Utah are other fantastic options if you like the heat. The Oregon coast is a wonderful place (Seaside, Cannon Beach, etc.) as is Seattle, Mt. Ranier and Mt. St. Helens and the Olympic Peninsula. The climate isn't harsh and there are lots of interesting and active things to do.

I'd try for yosemite, grand canyon, red woods, Southern California (Disneyland & Wild Animal Park) and Washington D.C.

I suggest skipping New York. Too much like London to be of real interest.

Utah! Zion and Arches National Parks in the south are amazing with their red rocks and canyons for hikes. In the north are the Rocky Mountains. Lots of movies are filmed there. It's very beautiful and the people are nice. It's home of the 2002 Winter Olympics, and you can learn about Mormon pioneer history. It's a great contrast to places like New York or somewhere on the coast.

I was born in Iowa, spent my childhood in Utah, and live in Southern California. Utah has absolutely spectacular National Parks - red rocks, blue skies, crazy rock formations. Seriously amazing. I would probably recommend Zion and Bryce over Arches in the summer - all will be hot, but Zion and Bryce will be SLIGHTLY cooler. But it's dry heat, which to me is much more tolerable than humid heat. But the Rockies to the north are equally stunning in their way, and the temps will be heavenly. Oh, and the smell of fresh wildflowers in the mountain air...there's nothing like it.

I've spent a fair amount of time in the midwest and on the East coast during the summer, and it's hot and humid. My favorite summer memories on the East coast are in Maine - I seem to remember moderate temps, beautiful, welcoming, towns, and lovely hiking. But I'm no East coaster, and they will have much more to say on the matter than I do.

California, of course, has lots to see - I second the motions for Muir Woods and San Francisco. San Diego is great in August - still crowded, but temps are mostly moderate. The ocean is of course lots of fun; there are lots of amusement parks if that's your thing; Balboa Park in San Diego is one of my favorite places in the whole world. Lots of museums, fountains, places to run around, etc.

I also second the recommendations for Oregon; I especially love Cannon Beach, too. One of my all-time favorite vacations was to Washington to the San Juan Islands - SUCH beautiful scenery, perfect weather in the summer, lots to see and do between the different islands...just gorgeous.

I haven't traveled much in the south. New Orleans was amazing in the spring, but I think it would be hot and not very kid-friendly in August. I couldn't breathe in Texas in the summer - TOO hot and humid. I went to Florida in the winter, and loved it - but I don't know how it is in the summer.

But if this is your chance to visit, it's your chance to visit - don't let weather *stop* you. I would just say that especially with kids, there are still so many amazing places to see that AREN'T deathly hot and humid, so it might be nice to spend more time in the temperate places, and leave the hottest/most humid places for another time or for very quick stops.

I love to travel, and always think that it's more exciting to travel internationally. But reading this and reflecting on past vacations...the US has so many amazing sights to see, right here in my own backyard. Thanks for reminding me!!

i live in south texas and its humid and hot. not just normal oh its warm out its like car seat brun your bum hot. and your wet all day from the sweat and humidity. not sure what its like up in the pan handle. i saw some picture so spokane washington and was blown away...as soon as i get around to it (making more money) i am definatly headed that way.

I think the West is the most forgiving in August as far as heat goes.. You should definitely go to Yosemite. San Diego is great (I live here!).. you can hang out at the beach on Coronado (always on a top 20 list for the US) and the kids would love Legoland in Carlsbad.
The Northwest (Seattle) is also beautiful.. you can go to Pike Place Market, ride the ferries, go hiking.. Napa Valley in northern CA is beautiful.. not too much for kids but it is pretty.
Of course, I'd recommend NYC for the east coast.
If you do come to Southern CA you could rent a car and drive to Las Vegas.. it's a 6 hour drive away and you'd get to drive through the desert and see lots of nothing :) Which is nice sometimes... then just drop the car off at a rental place in Vegas (planned ahead of time of course).. There's lots of shows for kids to see..
Plus! The Grand Canyon is not far from Las Vegas along with the Hoover Dam.. those are a good 3-in-1 deal.. Las Vegas, Grand Canyon, Hoover Dam.
It will be hot out there in August but it's worth it if you don't know when you'll be back.

PS- The Wild Animal Park is now called Safari Park. They changed the name.. it is a lot of fun if you're in San Diego. You can even zipline over the animals!

Start in NY city, then drive west to Niagara Falls and Chicago. From Chicago, fly to Seattle, then you can either fly or drive south to San Francisco. From SF, drive (or fly) east to Las Vegas and Flagstaff (to see the Grand Canyon). Drive to Phoenix and from there fly to Washington DC. From DC you can drive to Philadelphia and then back to NYC. With this itinerary you will see great cities during (almost) the best time of the year to visit most of them. I left out a lot of cities in the South and Southeast because of the weather in August (too hot/hurricane season).

Here's a Google Map of this itinerary:
http://maps.google.com/maps?f=d&source=s_d&saddr=New+York,+NY&daddr=Niagara+Falls,+NY+to:Chicago,+IL+to:Seattle,+WA+to:San+Francisco,+CA+to:Las+Vegas,+NV+to:Flagstaff,+AZ+to:Phoenix,+AZ+to:Washington+D.C.,+DC+to:Philadelphia,+PA+to:New+York,+NY&hl=en&geocode=FXFAbQIdK8KW-yk7CD_TpU_CiTFi_nfhBo8LyA%3BFeSRkQIdubBJ-ym3M-Yp6mPTiTGzqsW55FqXYQ%3BFWICfwIdGuDG-inty_TQPCwOiDEAwMAJrabgrw%3BFcJp1gIdWVy1-ClVM-iTLBCQVDGa1URpRmUlEA%3BFVJmQAIdKAe0-CkhAGkAbZqFgDH_rXbwZxNQSg%3BFdYQJwIdMJoi-SnRffWkgre-gDGjebPV5tXMOg%3BFUghGQIdL4VY-SkxJi7a944thzEAs9vOoTwfjg%3BFblh_gEdy-JR-SnLeaFQ7RIrhzGsG0o1-MdpjA%3BFQh-UQIdsoRo-ylb5PZa3sa3iTEqXYjUIkVSwg%3BFc-fYQIdcxeF-ynrS7XU2LfGiTHBWD6M2BT1iQ%3BFXFAbQIdK8KW-yk7CD_TpU_CiTFi_nfhBo8LyA&mra=ls&sll=40.57386,-98.699925&sspn=23.583009,57.084961&ie=UTF8&z=5

Yep, I also recommend Zion's or Bryce Canyons in Utah. The scenery is absolutely amazing and unlike anything you've ever seen. Northern Utah also has some neat sites - Park City has lots of fun activities in the summer like zip lines, the Alpine slide, horseback riding, cross country skiing, hiking, etc. Salt Lake City is the capitol and has lots of historical sites to visit for free and not-so-free (the Discovery Children's Museum is a blast for kids and is located in the Gateway shopping center in downtown Salt Lake.)

Jackson Hole Wyoming is about 3-5 hours north of Salt Lake and is fantastic for mountain views and camping in Yellowstone. Plus you will get to drive through some of the amazing mountains we have here. California mountains have nothing on the Rockies!

The Oregon coast is absolutely gorgeous and worth a visit. Disneyland is not (I was just there, so not impressed, and in August it will be hot, packed, and yucky.) I would avoid Vegas (in August? I'd rather die) - it is SO not child friendly. Shudder.

Janine here. Thank you all so much for all these ideas! I thought you might all laugh my question, It was a bit vague - the US is so vast! Obviously we had worked out a basic itinerary but with all these suggestions there may be some changes he he! I particularly want to thank you all for taking the time to write such detailed answers. I'm sure we'll have a great time, whatever we decide to do. Perhaps I'll write a post about our trip next year and let you know how we get on!

Thanks again!

If you are going to be in or passing through St. Louis, I can not say enough good things about the City Museum: http://www.citymuseum.org/home.asp
Serisouly, it is unlike anything in the world! Ten story spiral slides, caves, tunnels, a giant whale, amazing climbing structures, a ferris wheel on the roof, and even a shoelace shop. And it is all made from re-used materials! It is part art project, part jungle gym, part museum and wholly awe inspiring.

And it is not too far from the St. Louis Arch and the St. Louis Zoo is great too (and free!). Have fun!

I'll echo everyone who suggested Bar Harbor, Chicago, and Yosemite. A little of everything, but you have five weeks! :o)

I'm in Chicago, the weather here can be unbearable in August. Or beautiful...you never know. Be sure to research the climate of wherever you think you want to go!

Itinerary really depends on what types of things you like to see. There truly is something for everyone. All of the recommendations above are excellent.

(This reminded me of some German relatives who visited once, and wanted to see the WHOLE country, NYC to Hawaii, in 3 weeks. They had no idea how big the U.S. is! I'm glad you already know that!)