I would say it's best to teach them the same way you teach them about money. Except for the bits about security. 
Kids are able to pick things up quickly anyway, so it shouldn't be too hard.
Kids are able to pick things up quickly anyway, so it shouldn't be too hard.
It would be nice if you teach them bitcoin the same way you teach them about money but don't forget not all kids are interested in bitcoin for such a reason that they are too young and playing and enjoying are what matters to them. On the other hand, if the kids are into it why not create a game like a game with story line, educational, puzzle and so on that will advertise the mechanics of bitcoin since they are morelikely to engage in technologies. Another way was to explain the concept of bitcoin in a creative way.