There are a few factors to consider. Does the school curriculum include basic sex ed in it's curriculm. If so, what grade? Your talk should come before that.
More importantly, is your child asking questions? Do you think he/she has the maturity to handle specific topics? Is there reason to think he/she is on the cusp of puberty and any physical maturity?
We began to talk to DS about puberty at the end of 3rd grade. He was almost 9 at the time. At that point talk was focused on the changes his body would be undergoing in the years ahead. Last year, in 4th grade, there was a group of kids getting heading into some fairly suggestive topics. DS came home with questions that opened the door to a basic sex talk. At the end of this year (5th grade) his health curriculm does cover puberty, physical development, reproductive systems and sex. We'll talk more prior to the school coverage, during and after.
at 11:42 PM on Dec. 10, 2012