For some time now dd 6.1 yrs has been asking why boys have willies and why girls don't. Obviously I can tell her about sex but I don't know if this is appropriate for her age. I have found the following books but I need to know if they are going to answer her question to her satisfaction or if there are any others that you would recommend.
Where Do Babies Come From? (Usborne Pocket Science)
Let's Talk: About Girls, Boys, Babies, Bodies, Families & Friend​s (Lets Talk)
How Did I Begin?
Where Willy Went
Thanks