Sometimes it tends to scare them a bit.
I have a few effects in a haunted theme, It freaks out some of the adults, except for my 8 year old niece, nothing scares her. There's one illusion I'm working on now, that's hopefully going to scare the living daylight out of some.
I'm very cautious at performing some of the effects in front of kids. except for adults and depends who they are. Also kids are very free minded and can see things that we don't and often can pick the illusion and how it works. I think as we get older we see less, which is an advantage for me. If the trick passes a kid, it will fool most adults.