Think of an animal to make it into (ladybird, pig, butterfly, bee) and get him to help you make wings etc.
DS1 made a man out of one when he was 4 (so in FS2 at school) and won the prize! He's sooo not artistic (then and now) that it was really lovely for him to win. I think they knew that it really was his own work
Top tip - don't paint, use felt tip, much more manageable.