He and I were in the office and I was telling my thoughts about sex in marriage.  Eventually my wife also came in and we just a had a very matter of fact talk about sex.  It went very easily I feel and I would do it again.  The more you can just be at ease about it the better it will go.  If you treat any subject with respect you can talk about anything with your children.  We even had a Gray's Anatomy, that I picked up at a library closing, we looked at. 

He hasn't had any question after 1  1/2 years of marriage so I guess we did ok.