1) Photos: A small book of photos for your kids to flip through when they miss you is a great thing to stash in a suitcase. You can use an online service to have one printed for you, but we vote for the inexpensive photo book at your local big box retailer. Maybe leave a few pages blank so they can add their own pictures from the time you spend apart.
2) Map It!: We've always had a large fascination with maps (and have been known to argue with the Garmin a time or two), but kids are always fanatics for a tactile representation of your location. Call and let them know where you're at for layovers and let them mark it with a pin or sticker so they can track you across the country, or the world. Make sure to mark where they will be located on the map as well. If you get really into it you could print out stickers ahead of time from your home computer of landmarks you might see or pass on the way. (Eiffel tower if your headed to Paris, exc)
3) Take Them On A Mini Trip: Without leaving home you can expose your kids to some of the things you'll see, taste and experience while you're away. Eat different cuisine, or show them different movies or flickr photos from the location where you'll be. Don't forget to explain simple things too, like what types of animals you'll come across. Even if you're just flying from Missouri to Texas, every kid will think an armadillo is cool!
4) Communicate: Kids will want to hear from you each and every day. Call them when you can, if you'll have access, try using Skype or video chat to let them see you while you're away. Even a quick upload of digital photos to Flickr that they might be able to view can be helpful. Send them postcards before you leave, set to arrive once a day. You can have a friend or family member put them in the mail for you so guarantee they'll always be on time. You can even mail them a box of goodies half way through your trip with fun things to keep them busy, puzzles, snacks, trinkets and other small odds and ends.
5) When You Return: Bringing back presents is always at the top of the list, especially when dealing with children. Go back over the map and correspond photos and things done while you were gone to each spot on the map. If you have time, stop by a one hour photo booth and print out your photos before hopping a plane back home. Having photos for kids to look at when you get off the plane is a great way to occupy them while you're waiting for luggage and suffering from jet lag!
Do you have a favorite way to help your kids out while you're away? Let us know in the comments below!