#1: Decorate the large box to look like a burrow that a groundhog would live in. Create trees, grass and other outdoor items on the box.  
#2: Have your child act as if the box is a barrow. You even pretend to be a groundhog coming out of its burrow to see if it sees it shadow. Directed light at the groundhog burrow and when your child comes out it will produce a shadow. Turn the light on and off to show and not show your childs shadow. If your child does not see their shadow they stay out of the burrow and can play.