This is just my opinion and not fact....
What is immoral is teaching them nothing! I would guess they need to be introduced to the basics at around 10, and have many follow up talks. They should learn to be open with you. I don't think soft p 0 r n is appropriate, but medical illustrations would be more proper. You do not have to do all the details right away, but soon they should know about self-gratification (they probably will do or have done it anyway) and that it is perfectly normal, natural and good for them in common sense amounts as each person is different, but to do it in private behind locked doors..
Especially for teenage boys, emptying the prostate 2 to 3 times a week is important in removing carcinogens that could lead to prostate cancer. Girls generally don't do much self-gratification as young teenagers. They should know about diseases and about safe sex. They should know that one sperm at the wrong time can ruin a life...and that it can go thru the fibers of clothing in a close situation. They should know that becoming friends with someone is important before they get intimate. They need to learn respect for their mate. They should know about cleanliness. Sex should never get in the way of doing homework.
You can use people you know that screwed up as examples of what NOT to do. The last thing you want is to have their friends teach them...cause it will be wrong and it may be too late! Kids at school are hung up on oral sex because they know they won't get pregnant, but most do not understand STDS or even herpes. Others just think an abortion is a simple procedure so it's anybody with a penis. So get there first and do your thing..
Teenagers will do what they are going to do regardless---you want to be sure they do it safely and intelligently.
You can be their source of anything they want to know. They will think that you are pretty cool.