Personally we think the the Horror Makeup show is hilarious and its a don't-miss for us. However, I do think that it is a PG-13 kind of thing. Many of the jokes will go over the kids' heads, and some of the more gruesome parts of the show might upset them. If you only have one day, I would make sure that you do everything they want to do first, and then only do the Horror Show if they are not overly sensitive kids and have some concept of how fake movies are.