Let’s-Read-and-Find-Out Science series http://www.harperchildrens.com/hch/LRFO/index.asp
Looking over the CM Living Science library, you will find a large number of Let’s-Read-and-Find-Out Science books. This excellent series provides an extensive and interesting introduction to science for young kids.
Dr. Franklyn M. Branley, Astronomer Emeritus and author of many of the titles, started the series in 1960. While some have gone out of print (they’re great vintage books to find at a used book sale) the series still has over 80 titles covering a broad range of physical and natural sciences. Level 1 is written for the preschool and kindergarten ages while level 2 is for early elementary ages (1st through 3rd grades.)
In general, the level 2 books start out slowly; then, as you read on, you realize that this seemingly ordinary picture book starts to present some really great science concepts. Many of them include activities right in the text (rather than at the end) demonstrating these concepts. While they are not literature, they are well written for their intended audience. The level 1 books are much simpler, serving to expose younger readers to science. These are good ones to borrow from the library.