I was going to say that's actually a G K Chesterton quote, but it turns out it's more complicated than that. Neil Gaiman himself said it was from Chesterton (when quoting it at the start of Coraline), but he wrote it from memory and didn't double check, so the original is worded differently. At least, that's how my quick googling claims the paraphrase happened. The misquote is pithier than the original so... is it now a Gaiman quote, even though it originates as an attempted Chesterton quote?

As far as I can tell, the passage he was thinking of was:

Fairy tales do not give the child his first idea of bogey. What fairy tales give the child is his first clear idea of the possible defeat of bogey. The baby has known the dragon intimately ever since he had an imagination. What the fairy tale provides for him is a St. George to kill the dragon.

• G K Chesterton, Tremendous Trifles (1909)