YankeeGran, I think perhaps an approach that starts from the point of view of his welfare might be the way to go. Suggesting that he will have problems making and keeping friends or might lead to him being teased and/or bullied.
Another thing has occurred to be, I might be well off the mark and I apologise if this offends but, if he is so pre-occupied by this behaviour might he have been introduced to it by someone else? I have no experience of such things but in my early years training we were taught that inappropriate attitudes to sexual behaviour (taken as part of a wider picture including signs of withdrawl and challenging behaviour) might be indicative of something else.
Do have that chat with your daughter, emphasise that all you want is this little boy to grow up happy and content. All the best.
Have any of you got all electric cars? Pros and cons please.
Army horses loose on London streets
Angela Rayner lashes out and calls Sunak “pint sized loser”.