There have been a lot of children’s book parodies over the years (I’ll be sharing some recent ones soon), but over the years, one book has been spoofed more than any other:

Why Goodnight Moon? Well, it’s been around a long time. It’s reached near ubiquity. It makes some bold style choices that are fertile ground for jokes. And it has a beautifully simple text upon which you can hang just about anything.
Proof!

…but do you know about Goodnight Azathoth, part of a series of Cosmic Horror picture books?
https://www.atlas-games.com/product_tables/AG2706
Hadn’t seen that one – added it in – thanks!