Four boxes, each holding a big and a small dotted outline of the same thing: a butterfly, a carrot, a cup and a moon. The child traces both, then colors the big one.
Tracing the pair back to back makes the size difference something a child feels, not just sees. The big butterfly takes a long sweep of the arm and the small one takes a tiny, careful loop, and that contrast is what sticks.
It doubles as fine motor practice. The small outlines are the real test of pencil control, so expect a few wobbles and plenty of pride when the little moon comes out right.