Halloween appearance for kids 3+ - could do with your help!

Hi, I'm going to be doing Halloween appearances (book readings) which are expected to last about 45 minutes. It's for a particular book which probably takes all of 5 minutes to read. I would love ideas of things I can do to keep the kids entertained but not too scared (as they may only be 3 or 4 years old).

There are loads of ideas out there, but too many to wade through. I'm hoping some of you may be more experienced in this area than me!