I am probably in the minority here but my parents told me about the facts of life when I was barely 5.
I had this kid's biology book (for example, saliva was described as lots of little worker men who broke up pieces of food) which my mom read to me at bedtime.
Anyway, I distinctly remember asking what the balls in the sack were for and she said she'd ask our neighbor for me (our neighbor was a doctor). The next night she came back with the answer... "That's where the sperm is made, sweetheart".
Is it weird, or a good idea, to tell kids these things before they are self conscious enough to feel it is an uncomfortable subject.
My parents weren't liberal nuts by any means though.