My son had a great time with this project because it was fun to paint with something out of the ordinary. I blew up 2 water balloons (one red & one green so he was easily able to know which paint to dip it in) and had him start with making the head of the caterpillar followed by prints for the body of the caterpillar.
Next I let him glue on on googly eye and some antenna that I cut from some craft foam.
Finally, I had him draw on the caterpillar legs. I got a kick out of watching him draw all the legs and he was trying so hard to draw them the same length.