Occasionally I allow my (toddler/preschool) kids to play 'Kindercomp' in DOSbox on my computer. It's got a mode that prints the letters you type across the screen in different colors, which seems to be the fan favorite because it rewards indiscriminate keyboard mashing.

When they get a little older I plan to introduce QBASIC programs that do the same kind of thing, then we can start looking at the code that makes it do that.