I was at a conference where an editor said she wanted “page turners,” so I have written my books in sections by page and aimed for 28 (of the 32) pages.
Other people have other suggestions.
3 Ways to Pace Your Picture Book by Joyce Audy Zarins
Lisa Rojany Buccieri and Peter Economy’s post on Pacing to Propel Your Children’s Book Forward
Pacing a Picture Book by Lynne Garner on PictureBookDen at blogspot