I find little guys are less willing to suspend their disbelief. I've tried twice this week to show 2 six year old boys a dragon book (which has pictures of dragon skeletons and musculature among other things). Both boys said "Cheez, you know dragons aren't real, right?". Mind you, one of the boys (my son) was doing charades last week, and said he wanted to do a person. "Now, it's going to be a person who is magic, and also real." It was Santa.