That one frightening image described at the end of eponymous's writeup (the picture of a rabbit flyfishing for a baby rabbit with carrot bait) is an allusion to, if not an outright excerpt from, The Runaway Bunny, the children's classic mentioned in dannye's writeup. It depicts the mother rabbit's response to her young bunny's threat to turn into a fish and swim away from her. There's nothing frightening about it to anyone familiar with The Runaway Bunny, which I remember as every bit as suffused with love as Goodnight Moon, perhaps more so.
As a child, I always found Goodnight Moon too tranquil, preferring the action and interaction of the characters in The Runaway Bunny. Now I appreciate both (especially the beautiful illustrations), but Bunny still holds the fonder place in my heart. Maybe there's some kind of fundamental Bert and Ernie/Calvin and Hobbes-type dichotomy between Moon and Bunny afficionados.