you can have them...
Crawl under a table with dangling specters
Mix a batch of Witches Stew, each child can add one item and stir.
Try a Balancing Act
Set up a trunk with costume pieces and have them get dressed up in a Halloween costume (over their clothes)
Have them guess what "body part" they are touching in the Mystery Bowls (do this at the end of the course so only those who have already completed the course hear the answers.)