Heather Has Two Mommies is a children's book by Leslea Newman, with illustrations by Diane Souza. As the title suggests, the book is about a little girl who has lesbian parents. It explains how Heather was conceived, by artificial insemination. Heather's teacher in school explains that there are many different kinds of families and that "the most important thing about a family is that all the people in it love each other."
The book has frequently been banned, not only for the immediately obvious reason, but also because it contains a description of the process by which Heather was conceived, which may not be appropriate for younger children.
Other childrens' books about homosexual issues include Daddy's Roommate, Gloria Goes To Gay Pride, and All Families Are Different. If you'd like to learn more about Gay Parenting, consult your local library.