4 years old son request to stay overnight with his cousin

My sister had a four years old son and lately he asked to stay overnight at his grandparents house so that he can play with his cousin (7 years old) who was back from Kuala Lumpur for school holiday. When my sister has to work in Kumon, she will place this son at this grandparent's house. My sister was in difficult situation as she did not want to leave his son alone. She asked his son to call his dad for permission. His dad works in Kuala Lumpur and will only travel home during weekend. His dad agreed so my sister left him behind and drove home with his second son who is 1.5 years old, sad. My sister was very upset as she had a hard feeling that her son starts to become more independent and willing to stay up with his cousin instead of follow her home. My sister had once advised his son to pursuade his cousin to stay with him at thier house instead her son stay at his grandparent' s house and her son told her the cousin did not want to. I tried to console her and one point that she struke me : Why a four years old son so easy influnce by others? Why he cannot stand on his point, his cousin cannot come so he has to stay? Cousin is so important than his son?

Hong Zheng is now two years old and how i wish he can grow up faster so that he is more independent. One day, when he really so independent i will feel loss as my sister. My sister told me, you must slowly release them else you are going to be very hurt.

Bring up a child will never stop thier parent's from worry.