A simple 3D printed spirograph, that fits just on the build platform of a Prusa i3 MK2 :)

Great gift for a child!

Edit: The holes have a diameter of 5mm, and the thickness of the spirograph is 10mm. It was made very thick intentionally, to survive rough handling by children. If yours does not need to be as sturdy, you can scale down the model in the Z direction, in order to make it easier to fit various pens through the holes.