Paper towel butterflies. I've also seen this done with coffee filter papers and a couple of egg box bumps for the body. Colour in then spray with water then let dry. Tada!!! (alternatively with clothespins instead of pipecleaners)
Mix grass seed in with potting soil. Fill up a nylon. Tie into segments with string to make a 'caterpillar." Soak in water till saturated. Then let the kids spray it with water every day after and watch it grow. When the grass gets "too long" let the kids give it a "haircut."