It may be Kourtney 4th child, but it is his first. I would imagine they celebrated the day with all the children. I'm sure she has pictures of herself with each one of her children individually. It's only natural that there would be a picture of the two of them with their new baby. It was his Instagram acc. I bet there are pics of them with all the children. She seems to be a good mother and I doubt that she would allow her other children to be excluded..
This is not his first child. He has children from his first marriage. He also was a father to one of his first wife's children who is not biologically his. Kourtney has no good reason to exclude her other children.
