I don't think kids can't grasp basic concepts to understand Bitcoin such as decentralization and a open sourced nature, no to mention p2p protocol.. etc. They can grasp the idea of money itself as a means to get stuff, but beyond that is too difficult to explain. They wouldn't get it, just like they wouldn't get how fractional reserve works, etc.
Depends on
how do you present this information to a kid. You can leave out all unnecessary and complicated details; it's enough for a child to know just a very basis.
If the kid is able to understand that fiat currencies are established and controlled by governments as the main store of value, then it'll be easy for him (or her) to understand the fact that some people decided to create their own money, indepented from governments, and empowered them with value too.
I totally agree with you. Almost everything can be explained to a kid, you just need to choose the correct wording.