A couple of years ago my mom did a kit through Junior National Geographic. Each month the kids got a kit that was focused on a country and included resource guides, cultural stuff, recipes, city info...just loads of stuff. The kids loved it and really enjoyed stamping their "passports" each month once they completed the kits.

I LOVED Cricket Magazine. It is geared toward 9-14 year olds. It is a wonderful literary mag, if your oldest likes to read this would be awesome. My kiddo is due in December and I can't wait for her to be old enough to enjoy this one. I just hope it is still around in 9 years.
I second the Junior Nat. Geo. I liked that a lot, too. Nothing is more fun for a kid (or an adult for that matter) than getting interesting mail. My mom gave me a subscription for my birthday and it makes me so happy, and I am 25.

The magazine was NOT Junior National Geographic, it was an age appropriate subscription. Not that I would mind a kid's mag at 25...

I second Cricket Magazine--and they publish several other magazines with different subjects for different age groups. My 7-yr-old who loves science adores Ask magazine. We also enjoyed some of the other Highlights for Children mailings; they come with workbooks, stickers, and puzzles.

we received a subscription to Animal Baby as a gift and our 2 year old daughter loves it. it is geared towards kids 1 - 4 years old. the website is nwf.org/magsforkids

I've heard great things about Little Passports. Each month your child gets a package "from" a different international destination. http://www.lifeinasippycup.com/2009/05/pack-your-suitcase.html

It sounds like this might be a great market for someone to get into. Maybe green crafts, user submitted stories, recycled material. I am willing to be that most of the packages out there are someone traditional. Maybe someone younger can come up with something that the cool kids would like.

1 on cricket. They have other magazines geared toward different ages.

I used to adore Ranger Rick magazine as a kid. Dunno if they're still around, but it was always a highlight when the mailman brought us that.

My 2 year old also loves Animal Babies.

We did Animal Baby- great magazine, tons of real photos and great illustrations; simple stories and games. Good for kids 0-5y. I feel that National Geographic for little kids are better for 3-6yo.

We also got Babybug magazine, it has rhymes and stories.

My DD loves animals so she's more impressed with the animal magazines.

One of our last remaining independent bookstores has a terrific book-a-month program. You can sign up online, so there is no need to ever visit the store. You complete a profile form for the recipient, and then a longtime staffer and book expert chooses a book-a-month to send to him/her. Details here (I am not affiliated with the store except for being a frequent browser and buyer, and I'm sure that other independent stores have similarly wonderful programs):

http://www.politics-prose.com/book-each-month-gift

On the magazines: I agree that Cricket is terrific, as are the magazines in the same line for younger kids (Ladybug, Spider, and Baby Bug, I think).

My kids also love the puzzle magazines from Highlights: Puzzlemania for older kids and Puzzlebuzz for younger kids. The ordering format is a total pain, though: you subscribe to a "club," whereby they bombard you with a bunch of magazines coming in every few weeks, billing you separately each time until you request by mail that they stop. We did this for each child for long enough to accumulate 8-10 magazines, and then just squirreled them away to be given out periodically. Perhaps too labor-intensive for a grandparent to take on.

Don't forget about "Highlights" or their pre-school version "High Five". We've been subscribing to "High Five" for over a year now and my son loves receiving it in the mail every month. We like it so much we gave a gift subscription to our nephew too.

"Your Big Backyard" put out by the National Wildlife Federation is a great monthly magazine. My son received a subscription to it from my parents when he turned 3 and is still loving it at 5. Besides the great stories and pictures there is a family fun guide at the back which always has a song, recommended book , a cooking together recipe and a craft project. He can't wait to get his magazine every month.

The science-oriented magazines Click, Ask and Muse (depending on the age group) eg.

http://www.clickmagkids.com/

Also I know it's kind of obvious, but there's always a Netflix subscription. You can open an account and given them their own queue to manage (you can set a parental rating on what can be added to their queue -eg. only allow PG films).

Have you considered FamilyFun? The magazine, now in it's 18th year, is packed with fun, hands-on ideas that keep kids busy and happy. It’s a “do-it-yourselfers” dream! And even though it’s written for moms, kids love it, too. My 8-year-old and 5-year-old love flipping through the pages each month and looking for creative ideas. Full disclosure: I work for FamilyFun as their digital manager, but I’m also a big fan. The magazine has a great deal for current and new subscribers – two subscriptions for the price of one. So you can get 10 issues of FamilyFun for just $5! http://bit.ly/2ZsdZY