We really like the Leapster. There are games that are fun and learning like Puzzlepower, or some work on math skills. My daughter really likes the Dora Camping one that works on Spanish skills. She, too, is reading at a much higher level. Having a few different games allows her to work on various skill levels. It is not just about playing a video game, but learning in the process.
We enjoyed sticker books on our last flight. Also, some reading books that are of interest to the kids. Don't forgot to fill up water bottles in the airport after you go through security. There just isn't enough stops with the beverage cart to keep one hydrated. And many have said, lots of snacks.
A deck of cards, Uno, Skipbo (they make one of Skipbo with shapes for younger kids) and other card games for young kids.
A dvd player is nice for longer flights. The Leapster games will also use the headphones that you use with a dvd player. If both kids want to watch, you might check into a splitter for two sets of headphones to be hooked up at once. It works great on ours.
Have fun on your trip. Don't forget to pack a couple of small games/toys to play with at the other end. We keep toys/games on hand that only come out for doctor offices (mine) and trips. This way they are new and keep them entertained for longer periods of time. Oh, pack a few books for nighttime reading, too. Each of my kids has a backpack for traveling and they keep their video game and activity books in them. I take the snacks and the dvd player/dvds.