Tons. Really. Back when I was 6 or so, I filled a whole around 200 page A4 notebook with a simplistic (a stickman walking on straight lines and fighting evil man-eating plants) platformer game, which I passed myself by drawing character's track with lines, where for example a loop in the line could mean a punch or a salto and so on. I lost the notebook long, long ago, but I have some Mario level drawings back home. I could scan them next week if anybody wants to see.