Bitcoin is difficult to explain. I also felt difficulties in understanding bitcoin for the firs time. Let's share how to explain bitcoin to children of teenagers. In My country I can say 98% children don't know bitcoin. In fact, bitcoin can be future money. If the children not familiar with cryptocurrency or bitcoin, how can they face the digital era in the future.
If they do have a smartphone, just teach them to try to open an account / wallet of bitcoin and give them a couple of money. I think from there they can learn a lot on how powerful the bitcoin is