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.
It is okay to tell bitcoin to teenagers but not really to children. As a young boy or girl, they must focus on their study rather than dealing with bitcoin. They are not so knowledgeable and wise enough if they participate on it. In teenagers, it is better to first have a research about it to have some backround.
I'm just afraid that they won't interested in Bitcoin. If they really want to know, tell them the basic first. What is cryptocurrency? Bitcoin is one of the cryptocurrenct but it is more popular than others cryptocurrency.