We ran across this Crinkleroot book series by accident when I was looking for books about birds for a FIAR study. We liked it so much that I got onto the library website and found that there were a ton more. Some are pretty simple and others are a bit longer. We’ve read a number of them so far and H is a big fan.
We’ve both enjoyed and learned a lot from them. I highly recommend you grab these from the library sometime! They’re great for science and unit studies.