It’s hard to be sure, but I’m guessing Margaret Wise Brown and Clement Hurd’s Goodnight Moon, which clocks in at 32 pages.
Go the Fuck to Sleep is also 32 pages, and I’ve read that one too. (There’s also a child-friendly version called Seriously, Just Go to Sleep. Just imagine the first-day-in-Diagon-Alley moment when today’s toddlers grow up and discover the original!) But Goodnight Moon is the original 32-page bedtime story, so it’s got place of pride in this book challenge.