It is art and children love art. They draw things they know and know recently but they even don't know what it means technically. Children are hungry to discover new things and if they have fun with new things, they love it.
Children loves art and whether the story is real or fictional, the core message the OP is trying to pass is that whatever you do have a way of influencing or rubbing off on those around you. This is the case with the kid in the OP's story. Now, if this is happening with the kids, I can say that his mother will also feel the bitcoin effect. For the father to get the kid interested in bitcoin, he could start by telling the kid to recreate the bitcoin logo as well as other cryptocurrency logos. This would be a great way to spark a conversation about bitcoin.
Perhaps they did what is on their mind and the Bitcoin logo seems attractive to them. But for sure these kids never know what is this for, probably they just saw it on the internet or flashing on the television and it catches their attention. Education and some sort of introduction to Bitcoin is a good idea so these kids are also aware of the logo they've drawn but not necessarily they put weight on that.