OP I'm with you totally on this, and having read through the thread now, am alarmed and kind of shocked at the cavalier and casually louche attitude towards drug use that many posters seem to have. Yes I'm also very sheltered then, as I also wouldn't want anyone near my six year old taking any kind of 'pills'. (Perhaps because I don't live in London ... ?! 😅) I have a late teens SD and have heard a few things, so know that taking things like ketamine, ecstasy, cocaine and I don't know what else is rife among young people. Sounds like some parents too look on it as standard. (?!!!)
It's pretty awful people are trying to make you feel you're overreacting or being just some sort of idiot/bluestocking/interfering meddler who is out of line. I think you're completely right and it's v good of you to be concerned and feeling responsible as this little boy's father has a 22 yr old girl around who died my sound properly responsible. It doesn't matter if she's a girlfriend or babysitter or step daughter or whatever - she's charismatic, the little boy adores her, and she's a casual drug taker. She just doesn't sound responsible enough.
Would I want my six year old in another city with her? No bloody way.
Yes I think you should say something. This isn't judgemental - this is practical and reasonable and keeping a child safe.
I think you should talk to the father first. Raise your concern. Maybe also check out what he thinks his ex would think about it. But probably this girl isn't going out of the child's life. So the father needs to take the girl to task. Tell her he doesn't want this around his kid.
When I think about it, it's also to me totally wrong that this little bit should be hearing about drug use, however recreational. It's awful. Horrible.
If you don't get the right answer from the father, yes I'd tell the mother. Ultimately this needs to be dealt with. It's not ok.