The interesting way to teach children about bitcoins is faucet site. Just open and give them a faucet site. Trust me , they will enjoy claiming bitcoins. If your child likes playing video games, then give him a gaming faucet to claim. There are a lot of gaming faucets out there. Children will like that. In that way they will be introduced to bitcoins and slowly they will start to learn how to use bitcoins, how to do transactions with bitcoins, its specialities  etc.