How about getting a large refrigerator box and having some kids decorate it as a hotdog or popcorn stand?
Have kids make clown faces to hang on the wall. They could either color them or make them from cut up shapes. Kind of a cool add on to that: If some one (older child or adult) could paint or draw a large clown (on roll of paper), then you could have some kids cut out or decorate balls the clown could be juggling -- maybe you to add a writing assignment to this and on each ball have the kids write something about your school values or mission (like empathy or leadership, etc.).
Have fun. Would love to see pictures of whatever you end up doing for decorations~! (you could download them to your profile)