The best way to teach them is through games. New generation of kids are way more smart than us, games should be made which shows bitcoins instead of money and also show its uses.
Faucets are like games and for sure they are going to understand on how bitcoin works through it. But that's only a good introduction for your kids to teach things by things about bitcoins. And be careful on what you teach them because we know that there's gambling and it's not good for kids to know and use it that way.