It seems that kids really are growing up faster than they used to these days. I'd much rather educate them on these things than have to deal with the mistakes later.
Or we could work to correct why children are considered "grown up" when it comes to sex by second grade. I think there is something wrong with that.
I personally don't have a problem teaching youths responsible notions about sex (ie it may be a bad idea to engage in sex outside of marriage/or committed relationship [and basing those reasons on concepts that aren't really religious], but if you do, take precautions A, B or C...)
Perhaps 2nd graders are a bit young...but if they're capable of understanding, why not start teaching them responsibility?