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.
I agree if you want to teach kids about bitcoin you should always think and express to them bitcoin as a money because it has value and it has price so it is very important. And for me it will not be so hard to teach a kid about bitcoin because most the kids nowadays are technology inclined it means they can easily manage to adopt to a something that is spread by the internet or technology base. So for me as developed and grow they can also develop their knowledge about bitcoin and how they can earn more through it. Kids are able to pick things up quickly anyway, so it shouldn't be too hard.