We went to the bookstore and library, and I was very disappointed with the selection of books on the topic for this age. Ultimately, I checked out a video entitled, "Where Did I Come From?" The video uses cartoon characters, but is very explicit. Is there anything else out there for this age? What do I say to my daughter?
Young children don't want or need explicit details about how reproduction takes place. Usually a simple answer is sufficient: "Mommies have little cells already in their tummies that can grow into a baby. Daddies have little cells, too, and when mommies and daddies love each other and get really close the cells come together and a baby starts to grow." Your daughter will take only what she can absorb from this, and as she thinks about it and has other questions she will come back to you for more information.
Be sure that whatever you tell your daughter is honest and as accurate as possible. Parents who talk about storks and cabbage leaves create children who eventually realize that their parents lied to them. You want your daughter to have correct information, and you also want her to feel that she can come to you when she has questions and that you will be honest with her.