I think the fact that the OP was asked to visit earlier than planned, speaks volumes. The parents are obviously not coping well and this little boy is bearing the brunt of it. Punishment is not the answer here, as he’s only reacting to obviously feeling left out - and breaking his toys is cruel, unwarranted and will only make things worse.
OP I think you need to talk to your daughter and son in law about what you’ve seen and how disturbed you are. Point out that their behaviour will inevitably cause the boy to resent his sister and it will make things so much worse. While I don’t agree with a PP who said that the boy should stay with you, I think that maybe while you’re staying with them, you could take the lead in involving your grandson in day to day routines with the baby. Hopefully this will make him feel a bit more included as well as strengthening the bond with his baby sister.
Labour Brings in excellent Renter's Rights - long overdue.
News blackout on Old Bailey Starmer arson case.
April 22nd Limerick (July '21 & July'23 AND....)


