Actually I liked this even more than Hiaasen's 'grown up' books. It's pleasantly short (though not so short as to be unsatisfying), with a tightly plotted story.
The plot is a real page-turner with a great cast of characters. The jokes work on two levels: the subtle ones that Hiaasen slips under your radar and then the funny set-pieces (no, I'm not going to include any spoilers!) with lots of physical gags.
The bad guys are well drawn, not just cardboard characters - the only one I found annoying was the hopeless police patrolman who was just a little too cliched. The school counsellor will send shivers down your back, and the building site manager is very funny - we've all met or worked with someone just like him!
I'd highly recommend it for anyone, probably the youngest at about 7 or 8 if they're a confident reader, but adults will love it too. I find Hiaasen's adult books a little *too* cynical but this struck exactly the right balance between cynicism and hope. A very satisfying read all round.