We are not meant to be "perpetually solemn," according to C.S. Lewis. "We must play." This is something children understand instinctively. They don’t even have to be reminded to play. They just do. Part of growing up is realizing that there are times you shouldn’t be playing, of course, but part of growing up ought to be remembering that there are times we should!
The spirit of play is part of the creativity of rest. Little kids get out of breath. They get flush cheeks. They come falling into the door at dinnertime after a long afternoon playing in the neighborhood smelling like little puppy dogs. They have skinned knees and grime under their fingernails. There are rocks in their pockets and grass stains on their sleeves. Their hair is messy and their eyes are wide. It’s hard work playing so well. They cannot wait to get back outside and do it all again. This is all so God-glorifyingly beautiful.
The average eight-year-old boy on your block is a little Michelangelo of play. Take his toys away, and he will make a tower with the cushions, a battleship with a cardboard box. He will have at you with a wrapping paper tube. (And his little sister throws the most delightful tea parties for invisible royalty the likes of which no fairy tale could ever imagine.)