The mother chose to leave your son and her daughter. She may be building a life and want involvement now. There is a new partner who is a stranger to the little one. All this is a lot for any child to take in and can be generally upsetting.
The child's welfare here is most important this is a delicate situation your son should set the boundaries for visits. A timetable whereby his daughter spends a limited time there with no pressure to stay.
This can be arranged in family court if necessary without the need for the little one being asked questions. Which can in its own way be damaging and confusing she is very young. If she is only wanting to be with her daddy overnight so be it that's where she feels secure. You may also see a change in her behaviour after a visit as a happier child.
Good Morning Thursday 14th May 2026


for the OP.