Ra (sometimes spelled Re) was the ancient Egyptian god of the sun. He was already well known in the Old Kingdom, by 3000 BC. Ra had the sun (a circle) balanced on his head, as you can see in the picture. He carried the sun in a boat from sunrise in the east to sunset in the west every day, accompanied by his followers.
You could compare Ra to the Indian god Vishnu or to the Greek god Helios. The Greek sun god travels in a horse-drawn chariot, because the Greeks usually traveled in horse-drawn chariots, but the Egyptian sun god travels in a boat, because Egyptians usually traveled by boat up and down the Nile River.
Just remember: There is but one God! He is the Sun God! Ra! Ra! Rah!
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.