I'm not a parent, but teenagers tend to have sex. It's just the nature of reality. It is perfectly natural for them to desire to, due to biology, and thus, many of them do. I don't think they are going to stop just because their parents don't like the idea. You can advise them, but that's about it. Hopefully they will make good choices, and if they have sex, hopefully, you have taught them about safe sex, and hopefully, they will listen. I would not advise telling their parents, as their parents might handle it badly and it could be very emotionally upsetting for the teenager. Personally, had someone caught me having sex as a teen and told my mother, it would have upset me VERY BADLY emotionally. I would be riddled with embarassment, shame, guilt, depression, anger, anxiety, etc. I am not saying I would stop having sex. I am saying it would send me into an emotional rollercoaster, and not to trigger anyone, but I probably would have SI'd. To me sex is very personal, and it is not something I want my parents to know about. My sex life is something I think my parents shouldn't have intimate knowledge of. And my mother and I were NEVER open about sex. We are just not comfortable talking about that sort of thing. Until recent years, talking about my period with her made me uncomfortable, even though I could tell men about it. I have just been taught to be ashamed of sexuality within my family and so I don't like discussing that. Also, please consider not only the emotional number it will do on the kid, but who knows how the parents will react! They could make the child have a very unhealthy view of sexuality AND themselves because of it. They could even become verbally or physically abusive over it, or get really controlling, overprotective, etc. and forbid the child to ever leave the house. I mean, it's just not a good idea to tell parents something that get so many people so upset (many people freak out over their kids having premarital sex, to an irrational degree and may get really angry and unreasonable) when you have no idea if that parent is abusive or not, when you have no idea how sensitive the kid is to this type of thing, and when it is extremely common and even natural and normal for teens to be doing this, even if it's not advised, and when the truth is, they will likely continue to do it, anyway. This probably will not stop them if they really want to have sex. I know people whose parents flipped on them over having sex as teenagers- and they never stopped having sex. Also, some parents don't want to know. One person I knew told me that they knew their children would eventually have sex, and that they knew thier kids were informed about safe sex, and they just hoped their kids would have safe sex, and make good choices, but that they really didn't want to know when their kids had sex and they also weren't going to tell their kids whenever they had sex, either. It was a personal thing you didn't tell such close relatives about. You knew they would, they knew you did, but you didn't discuss it because it was private.