Small Rant on Children's Books

Why do books aimed squarely at young children have to include language that isn't appropriate? Last night, my seven year old was happily reading the third book in The Spiderwick Chronicles, Lucinda's Secret, when one of the children in the book says, "Oh, crap!" Now, I ask you, is that necessary? Other than this, the books are wonderful depictions of fantasy characters and children doing things that they certainly shouldn't, but make their intended readers happy. I'm not asking for artificial speech, but not all children are using epithets.