To not tell her parents?

Why would you even consider keeping this a secret. No way.
It’s not the age, it’s the deceit.

Just checking, are you saying parents are expected to stay up all night on watch when their children have friends for a sleepover? And going to bed yourself is ‚irresponsible‘?

I agree that the other parents need to be informed, but to accuse OP of having done something wrong for it to happen at all, I think is a bit much.

Back when i was a teen it wasent uncommon for some girls in their mid teens to have boyfriends who were late teens early 20;s now that was awful and people turned a blind eye
Two teensgers with three months between them is not ideal but its not shocking like some posters are making out.

I agree. If you overdo it with the wagging telling off finger at kids it all goes completely underground and they tell you nothing. this isn't the sort of 'them' and 'us' relationship I want with my children. There must be trust and some guidance but overdoing the whole thing just makes them feel ashamed and like there's no safe place.

Who are you referring to as “frigid” then? Your posts says I have never heard the term pearl clutching used as a synonym for frigid

In everyday language, “frigid” is frequently used to shame, dismiss, or insult a woman for rejecting sexual advances, setting boundaries, or appearing emotionally distant and unapproachable.

Her parents need to know ... who cares if she's nearly 16?? Just because it's then legal, having sex at a FRIENDS HOUSE in secret with her family in the house at the same time, is plain wrong and very very immature. They need to know so they can instil in her this isn't normal.or appropriate behavior. They need to know.

In what way did my comment say that anyone should support underage sex? I said it's not ideal BUT my recollections of my own teenage years were many of us were at it AND if it was my own teen the context (safety, consent) would be more of a concern than their actual age if it was a matter of a few weeks.

I am NOT proposing people should be actively supporting or encouraging their underage kids to have sex. But I AM saying some of the comments around how utterly horrified and outraged her parents should be and accusing the OP of supporting statutory rape feel a bit OTT and, for want of a better term... pearl clutching.

Also agree with this

I agree with this.

I think I would tell the parents everything I know: that the kids snuck a boy in and that I have been told they had sex.
Do you know 100% what happened? No. You only have unreliable teen say-so. But this was under your roof. You were the adult in charge and they snuck this by on your watch. If this was my child and I found out that other parents knew and didn't tell me, I would be furious. You need to be honest and model that honesty and accountability for your daughter.
No judgement in it, just facts.
They might initially be angry with you for 'letting it happen', you'll have to take that on the chin. It wasn't your fault and teenagers are resourceful and all kinds of sneaky! It's their whole schtick.

Indeed im nearly 53 and didnt have sex untill i was 18
But i know pleanty of people of the same age who did have sex at 16 or under
Both were normal.

If you don’t talk to the parents, you’re showing your daughter that sneaking a boyfriend in and having sex with him is no big deal. Is that the message you want to send?

Telling someone sex outside marriage is wrong is just as shitty parenting as allowing a 15 year old to have sex (which isnt what the OP did).

Happy to dive into how the English language works here.

Referring to something in this context as 'being normal' - means 'not unusual'. The word doesn't denote a majority status. In this context it could also be 'normal' (not unusual) to not have a boyfriend.

It wont make any difference despite whst some mumsnetters think should hspoen
As they are so close in age its not in the public interest for the police to prosecute .

But he’s 16

Nope. I mean you calling other women “pearl clutchers” for not being cool with supporting under age sex, are you saying not supporting underage sex = frigid?

You think it needs investigating?
OP could literally ask her DD.
And the DD would clearly have mentioned if the boy was rapey anyway.
I think likening this to a sexual assault on a child (which i suffered age 7 by a 40+ male) is far beyond ludicrous.

This is exactly what I'd do, id explain the situation, that she'd snuck the boy in through the night and you feel they should know as you didn't have eyes on them and leave it at that, if the family can't sort it out between themselves from there then I think you've done enough to put them in the loop, that said if the mum asks you outright if you know whether they had sex I wouldn't lie and would say it's very much sounding that way but she should speak to her daughter. The reality is, whilst this happened at your house and you were responsible for them, you're not responsible for her having sex, this may not be the first time and even if would likely have happened elsewhere very soon anyway and the parents would be absolutely none the wiser but it's right that you give them a bit of a steer as this was your watch. Also not your fault btw that they abused your trust and home

I have never heard the term pearl clutching used as a synonym for frigid if that's what you mean. I tend to hear the term used in the context of false moral outrage? Which is the tone many of the posts on this thread have and I was referring to.

Sneaking boys in - not ok
Having very slightly underage sex if it's consensual and safe and with someone age appropriate - not ideal but definitely not moral outrage territory

Then why have you specifically stated.So in your social circles it wasn't normal to have a boyfriend until after you were 16?
so you were only “normal” if you were having sex if under 16?.

Your other child/children were left very vulnerable, basically you had an unknown male in the house overnight.
Tell her parents and I wouldn't allow another sleep over.

Not everyone’s life experience can be applied universally to everyone else across different generations.

When I was at school in the early 2000s a lot of girls lost their virginity at 15.

Some of the reactions are honestly so bizarre talking about crimes being committed. If you go to the police and tell them your 15yo had sex with a 16yo they would do absolutely nothing. Those laws are to protect children from adults, not to criminalise teenagers who have sex with one another

You tell them so the parents have a chance to coordinate emergency contraception, I highly doubt they were properly protected…from pregnancy and all the other harms

It would be pretty easy to do if there was a group of them and you weren’t watching their every move (and why would you be?).