Samantha R. Vamos, writing at this site that I find to be a fine connector, Authors Now!
suggests every gift to children be a book.
In my elementary school-Mom days, I modified that for awhile, by giving a book AND something else.
A book and a stuffed animal.
A book and a set of magnets.
A book and a Harry Potter jacket.
A book and candy.
If you are looking for picture books about science one idea list to look at is here: