I'm one of those unicorns who has had what I would consider a pretty large number of partners and very few regrets, I guess. I regret a few of them because things didn't work out as I'd planned but that was usually a situation of me not being right for a person I was in a relationship with. I rarely regret a one night stand because I used them for what they were - an excuse to get off and maybe have some fun - and didn't expect anything more.
I know some women (and men) regret these things but I don't. I have plenty of experience and learned what worked for me. Turns out I have a very high libido and I need a partner who feels similarly. My number of partners is not something I'm ashamed of. My fiance knows that I've had far more partners than he has and he doesn't care. It doesn't squick him out. My libido doesn't freak him out. And while I'm much happier in a committed relationship for a variety of reasons, I don't regret my past.
I would tell his daughter (in the not so distant future as she's 8) or any future daughter of ours that sex is something best done when you are ready and you know what you want out of it. I would also say it's best to start off with someone you know really well but I would also actively teach that slut shaming is not okay. I don't think you have to say, "It's okay to fuck a lot of people". I think you can teach "slut acceptance" in a million other ways. I would basically do what my parents did with me which was freak me out just enough to realize how important the decision to have sex was from a physical and emotional view but also let me know it was *my* decision. I was a late bloomer (21 when I had sex) but I was fully prepared for it!
I can't be the only one, though.