Playing doodle-art was the game, when I was a child, that taught me to draw!
My mother called it 'Squiggles'. We would take it in turns to draw the 'squiggle' and to create something from it.
A more artistic way of saying this might be 'doodle-art'.
Doodles are little scribbles done in the margins of one's exercise book when bored - often very free and creative, for being made when the conscious mind is engaged in something else (a phone call, for example.)
If you google 'doodle-art' you'll see many examples similar to the one you have given:
And here is how to play 'squiggles':