Books for a very advanced 3rd grader (elementary school)
One of the best is The Golden Book of Chemistry Experiments.  By today's standards, this book is considered "dangerous", but keep in mind that it was written for teenagers in the 1960s.  In any case, parental supervision should always be required in chemistry, and if you carefully research the experiments before doing them you should be fine.  It takes you all the way through technique, building apparatus, and safety.  The only problem is obtaining chemicals: the sources cited therein are hopelessly outdated (i.e. your will NOT find most of this stuff in drugstores anymore), and you will need to use educational supply companies to obtain small quantities of chemicals.  Have fun!