Blind we are, if creation of this clone army we could not see. --Yoda

Kids. Small people who find absolute happiness in doing the simplest things. They will crawl into a corner and sit for 20 minutes taking sips of water and then letting it drool down their chins and soak their shirts. They take delight in blowing spit bubbles. They squeal with excitement at the ability to squeal with excitement.
Grown Ups. Kids that have grown up and forgotten that they ever found joy in these seemingly absurd activities.
Then they have little creatures of their own that follow them around and do things like drooling their water down their chins and creating puddles for them to clean up. They try over and over to blow spit bubbles. The successful ones get giggles of pride. The failures result in dirty looks from mom or dad or whoever was close enough to get the resulting spit spray in their face. They also get really close to ears who happen to be in the wrong place at the wrong time and squeal with excitement at the ability to squeal in excitement.
Full circle. When Mom and Dad, weary after a long day of tending to the kids, limp off into a corner and space out. They find themselves drooling out of the corner of their mouths and blowing catatonic spit bubbles. A sense of dejavu washes over them.
So when you see your kids banging their heads against the wall and smiling, or spinning around in circles exhausting themselves without ever going anywhere, just think: We dont stop doing these things. We do these things everyday. Only instead of calling it "playing" we call it "parenting".