It's be like Monster Blood, they'd all find some magical alien goo and eat it in Jell-O form, and then realize they spontaneously turn into animals at uncomfortable times. And then there are aliens involved who made the goo and want it back, and they're going to find it by infesting every human on earth.
And yeah I agree, in the end it would be like an even bigger Invasion of the Body Snatchers ripoff...they'd all be back at school living their normal lives but they'd all be Yeerks, dun dun dunnnnn...
Phoenix you're so right, Scholastic's Goosebumps TV show and the Animorphs show have EXACTLY the same production values (hence why they both look like utter crap, and have the same horrible faux-creepy background music)...so very sad.