•  Parenting Magazine has a helpful article: Smart Answers to Kids' Sex Questions.
  
• Talking with Kids about Tough Issues: from the Kaiser Family Foundation and Children Now offer practical tips for talking with children ages 8-12 about sex, drugs, alcohol and more. Useful links to other websites and books to help you talk about the facts of life to children of all ages.
• Planned Parenthood has a section of their website that gives an outline of "What Children Need to Know" by age and a small list of books.
• And Advocates for Youth has a large section of recommended books for all ages as well as a age by age section of what kids need to know.

Many of the books highlighted on these websites mirror the Top Selling Children's Books on Health & Sexuality on Amazon. But be sure to read the reviews since some books may cover more (or less) material than your family wants.