teach em young. and make sure there is NO awkwardness about the subject. protection is open, the fact that sex is wonderful is open. the fact that ur parents have sex, a loving pleasureable, intimate activity is open. the fact that you use protection for good reason is VERY open. and the fact that guilt doesnt exist in such a nice instinctual process is open.
seriously psychological harm done due to negetive sentiments/lack of sexual contact at appropriate post pubertial age is one of the LEAST discussed psychological problems of today. usually due to taboo, or political correctness, or the non existing ties to the overwhelming problems of pedophelia/incest. when it is a wholly relevant topic having nothing to do with the last 3.
the amount of harm done is underestimated. and id hope to heavens that i dont put my kids through that{if i have kids in the first place}