Shame on those of you who thought that's where I was going with this. I mean for some fun time. Cut pieces of it for them. And hey, if it lands over their mouths, so be it. Another good thing to pack is a small hand mirror with a protective covering or case.
Mirrors are great fun for kids.
You might consider a hand-held calculator, too. Bring along a few tapes with kids songs that you know they enjoy. Singing is always a fun way to pass the time during a long trip. Place a box between or next to their seats that contains some little gadgets for play. If your children are prone to carsickness, books might not be the best idea.