I split up with my son's father 2 years ago, after a 10 year relationship. We had one son who is now 4.
Last year a woman he'd a 3 month fling with, got pregnant and had a little girl.
They are no longer in a relationship and she's had moved quite far away. He only sees the baby once every couple of weeks.
At some point my ex wants to explain to our son that he has a half-sister but I am reluctant to do while he is so young.
I would be grateful for any advice or perspectives on this. I don't want to keep it a secret from DS but I do feel that he is too young to understand how this other baby got here and what his relationship with her, is. Particularly because his father only sees her occasionally and because of the distance, DS would be unlikely to see her very often. Also, because my ex is not living with the baby's mother and their relationship has been rather fraught and unstable thus far, I don't really want to introduce the child into my son's life when there is a chance that my ex may not have consistent access to her.
If my ex and this woman were still together and DS could understand the baby's arrival in the context of his Daddy being in a new relationship and having a new child, I guess that would be simpler, but this isn't the case.
What do I do for the best? Just want my son to be happy and don't want to confuse him. It doesn't really help that we don't know anyone else in his class or circle of friends whose parents are separated or who have half / step siblings. When should I tell him and how should I explain it. HELP!