Benson, Sally. Stories of the Gods and Heroes. New York: Dial Press, 1940, 1968. A retelling of the stories from Greek and Roman mythology written in simple language, appropriate for elementary students.
The Gods and Goddesses of Olympus. New York: Harper Collins, 1994. A pretty introduction to the major deities from Greek mythology. Hercules is not mentioned, but this can be used to clarify some of the other characters.
D’ Auliere, Ingri and Edgar Parin. DAulaires Book of Greek Myths. Garden City, NY: Doubleday & Co., 1962. A comprehensive collection of the stories from Greek mythology8 with enough detail to tell the stories, but also simplified for a younger audience. Good illustrations which have a classical tone.
Evslin, Bernard. Hercules. New York; William Morrow & Co., 1984. This 144 page book is devoted to the trials and tribulations of Hercules life. It is suitable for most upper elementary readers. It is written in a easy style and while there is some poetic license taken with the story, it provides another source for independent study.
Fisher, Leonard Everett. The Olympians: Great Gods and Goddesses of Ancient Greece. New York: Holiday House, 1984. A simple text offering very basic information about the Olympians. A good title to have for student browsing purposes.
Gods, Men & Monsters from the Greek Myths. New York: Schocken Books, 1982. Another resource for children to explore about the myths. Contains a brief retelling of the story of Hercules as well as some very nice illustrations and a map of Hercules world.
Green, Roger Lancelyn. Heroes of Greece and Troy. New York: Henry Z Walck, Inc., 1961. This book give a fairly comprehensive account of all the heroes from Greek mythology. It is helpful in simplifying the stories so that they are suitable for elementary students.
Lum, Peter. The Stars in our Heaven: myths and fables. New York: Pantheon, 1948. Contains a brief discussion of the myth of Hercules as well as the identification of the obscure constellation of the same name. This source suggests that the legend comes from the Sumerian and Babylonian hero known as Gilgamesh.
@Ref:The Usborne Book of Greek and Norse Legends. London, Eng.: Usborne Publishing, 1987. A compact and handy overview of the major stories and characters from Greek mythology. It includes a who’s who section which describes them and another which gives their Roman counterparts. Also includes a similar overview of Norse mythology.