These are all very good picture books for children that feature monsters. I will add to this list as I find more.

Love Monster by Rachel Bright

Monsters Eat Whiny Children by Bruce Kaplan

The Monster’s Monster by Patrick McDonnell

Even Monsters Need Haircuts by Matthew McElligott

Some Monsters are Different by David Milgrim

Frankenstein Makes a Sandwich by Adam Rex

Wanda’s Monster by Eileen Spinelli