You guys are better at this hook thing than you've been letting on. Some more hooks, and some homework.
1. You enjoyed the author's other work.
Someone asked about the hook of Twisted, by Laurie Halse Anderson, and as far as I can tell its hook is: Laurie Halse Anderson. If you write two books as good and as popular as Speak and Fever 1793, you too can stop worrying too much about hook.
I'm reading The Spellbook of Listen Taylor, and so far I'm having some doubts. But I had to pick it up because The Year of Secret Assignments was fun.
Now let's be clear, a book has to be really funny to survive on this hook alone. I see lots of manuscripts in slush from people who seem to think being mildly amusing is enough. It's not. Ginger by Charlotte Voake is mildly funny throughout, and has a good punchline. But it's also about dealing with a new sibling, and that's something parents actively request in bookstores.
3. Something to figure out.
People love puzzles. From The Trek to Where's Waldo, from Chasing Vermeer to The Puzzling World of Winston Breen... not to mention, of course, all the mystery novels that are presented as mysteries. I love Peter Abrahams' Echo Falls series. But Absolutely Not is an example of a book with a cool puzzle aspect that needed another hook to bolster it.
4. Audience participation
There's some overlap with the last category, of course. But aside from figure-this-out participation, there are many kinds that are so great for young kids. Whether it's a refrain they can join in on, or a word that they can guess comes next from the rhyme scheme, or even a chance to point out where the illustrations are contradicting the text, kids love to be involved. eg Bob, I Ain't Gonna Paint No More, and Do You See a Mouse.
How about some audience participation right now?: What are the hooks in Edwina, the Dinosaur Who Didn't Know She Was Extinct and How Do Dinosaurs Say Goodnight?