As a Christian mama of 4 children, 3 girls and a boy, I never referred to books to teach my kids about sex- I'm not saying it's a bad idea- but I agree with the statement on this feed that they can be sterile- and not to mention all books do not work for all children. Don't get me wrong- we are a family that devours books. AFTER I had the 'talk' with my oldest, I gave her a cute book on puberty and taking care of herself and a book with a Christian perspective on abstinence, purity, following the crowd that I picked up at an event. But before that- I just answered her inquiries simply. The books I gave her were to remind and reinforce what I've already taught her.
Answer the specific question. That is all you need to do. Focus on the Family says "Just because your 5 yr child asks how a baby gets out of it's mommy doesn't mean you need to tell your child how it got there." I've always answered the specific question in appropriate detail using the correct terms and names for body parts.
Trying to explain the entire experience to a child that young will overload her..let her be 4 and just answer the questions as they come.
Dr.Dobson also recommended speaking to your child about sex, puberty and all the details between ages 8-10. They can process it better and by this age- all of those "questions " they have asked along the way have helped. If every time I asked my mom a question about my body, she wanted to give me this looong explanation and waaaay more info than I needed- then I'd stop asking my mama- and start asking my friends.
I had the "FULL" talk with my oldest when she was just about 10. I made it a mother/ daughter date night. For my daughters personality- I asked her questions and gave her details in the car- eye contact would have been too much for her- she even asked questions a little easier when her mom wasn't 'staring' at her. Then we went about our special evening- dinner, shopping- at the end I just reminded her I'm always ready to talk or answer any question she ever has.