Here are my two ABSOLUTE FAVORITE science books for teaching children.
Play and Find Out about the Human Body by Janice VanCleave is just plain awesome! It has wonderful experiments that are simple and FUN for preschoolers to elementary-age children.
If I had to purchase only one book to use in science ever, this would be the one (and after 20 years of teaching, I have purchased quite a few). It's not Magic, It's Science! by Hope Buttitta teaches science in an entertaining and engaging way that makes concepts stick for elementary children (and even middle schoolers). I just love this book!
Enjoy Science Week!