When I was a kid some friends and I discovered a way to leave secret messages for each other. We would scratch words onto the underside of a green leaf with a stick. When the leaf dried the message would disappear so only someone who saw it while it was fresh could read it.
We felt clever to have figured out how to do that and it fit in well with the sort of things we played.
Back then kids were free to "go out and play" with others in the neighborhood without adult supervision so, unlike modern kids, we used our imaginations and pretended things for many years. We might be cowboys, space explorers, animals, kings and princesses, pirates, or any number of other things.
I was lucky to live on a hill in a small town where we could climb trees, swing from ropes, throw pebbles in the creek, or run up and down our curving, one-way street without fear of traffic.
It's sad that today many older children only feel free to use their imaginations by playing video games because adults are always supervising them.
Of course there are still some kids who have discovered the fun of getting carried away into stories by reading books. And I hope the writing on the leaves of books won't ever disappear.