well kids like to play, so something that can bring together bitcoin and gaming
like puzzle that when solved reveal a private key for example
it is important that kids start to learn early some basic economy, at least something about income and expenditure
i heard about a new law for some countries that will make it possible(to teach them basic economy) in schools
if the game is like a puzzle is a game that sharpen the brain for children, the origin of the game do not fight games it does not educate children under age. then better monitored also when using the game.