If you have a toddler you are pretty much legally obligated to dress them up like an Ewok. Don't think, just do it.
Even if they can't pronounce "mitochondria" yet, they'll appreciate the funny squiggles!
Available at: Kitty Baby Love http://kittybabylove.com/index.php?main_page=index&cPath=1&zenid=0075e3b9a641dab649c1d1549f0d9dc6 ($3 each)
Real books cause papercuts and have too many words. Start off a little easier.