Maybe a sort of lightning testnet/sandbox where we could challenge kids to play a game based on building a bitcoin-like environment and trying to hack it.  

For example, if there are 30 kids in a class/lab, what would be the minimum number of bits for a private key to assure no collisions?

Building a hashing app/program to create the most leading zeros from a hash in the least amount of time using the least amount of energy.

Your role is villain and your aim is to hack the network and steal everyone's coins.

Etc.