Who was Horus?
Horus was an Egyptian god, originally from Upper Egypt(Southern Egypt). In the Old Kingdom, people thought of Horus as having the head of a falcon, and his name means "falcon" in Egyptian. The Pharaoh was the human form of Horus, and then when he died, the dead Pharaoh was the human form of Osiris. More generally, Horus was a sky god,the son of the sun god, Re. He was the god of war and the god of protection against evil. A lot of people carried good luck charms in the shape of the eye of Horus, to watch out for their safety.
But all that gradually changed with the Middle Kingdom. Now people thought of Horus as the son of Isis and Osiris. Horus was born when Isis brought Osiris back to life after Seth killed him. So Horus became a god of new life and rebirth, like the Greek Persephone or Dionysos, or the West Asian Attis or Tammuz, or the Christian Jesus.
In some stories, Horus also had sons of his own. Their mother was usually the same as his own mother, Isis. Mostly what Horus' four sons did was to protect the internal organs of mummies, just as Horus himself protected living people.
Gods and Goddesses of Ancient Egypt, by Leonard Fisher (1999). For younger kids.
Isis and Osiris, by Geraldine Harris (1997). A retelling of the story for kids.
The Egypt Game (Yearling Newbery), by Zilpha Keatley Snyder (reprinted 1985). A great kids' story about kids who pretend to be Egyptian gods and goddesses.
Religion in Ancient Egypt: Gods, Myths, and Personal Practice, by John Baines, David Silverman, and Leonard Lesko (1991). Pretty hard going, but it will tell you everything you need to know about Egyptian religion.
Isis in the Ancient World, by R.E. Witt (1997). Mostly about the spread of Isis worship to Greece and the Roman Empire.