I got my 1st sex ed class the last year st primary and it was the best I ever had.
We live in a very conservative place and hubby wasn't really given any sex ed.
My 6/7 yr old son is interested and aware. Making his 4/5year old brother aware. Now they have a sister they have confirmation things are different between girls and boys.

I too ponder this question and would be glad to hear what others have done.

We certainly don't have access to books along those lines which makes me cringe. Espc considering all the soft porn pics that pop up all over our internet sites if the proxy isn't working. Stupid great firewall