I think better to wait for them to grow up before explaining. Maybe some videos on bitcoin on youtube may help with the visualization.
For me it is easy to explain bitcoin to teenagers but not on children, Because i am a teenager who knew or who are doing bitcoin, and i know it easy to explain for all the teenagers what is bitcoin all about but first they need to be ready before they can pick up it easily and they need to motivated first in bitcoin so it will be more easy to explain and they can understand it more easy. I will tell them that in bitcoin reading is the best key so if they want to learn just read or research whats is bitcoin all bout for.