I was showing my 7yo daughter some classic arcade games. She asked if I could teach her to make a game of her own, and proceeded to describe the premise. You are a water sprite, catching fish and avoiding sharks. Blowing bubbles at the fish makes you lure them in; blowing a bubble at a shark gets the bubble stuck on its head for 10 seconds.
I fired up Scratch, and in 15 minutes, while the girl sat on my lap, I roughed out the catching and eating fish component. When it was time to quit for the night, she took a drawing pad into the bathroom and sketched out the next five or six levels before while allegedly getting ready for bed.
When she sketched out the PC’s home base, and added a locked chest that contains a key to a dress-up room, she realized that she had crossed over into a different genre, and said, “This part can be a different game.”