I have a pocket guide from National Geographic that is about backyard animals. There is also one about insects in that series. Here is a link to the place I bought mine from:
http://www.rainbowresource.com/search.php
Unfortunately they don't show any pictures on this website, but my ds really likes the book we have (he is also 3.5). Lots of great pictures and good, simple info. If you click on the info button on the link, it will better describe the book for you. The website says for grades 1-5, but I guess b/c maybe they are thinking that is how old the child would have to be to read it by his/herself.
