It makes absolutely no sense that a member of an order which forbids attachments would have a child when he had a front-row seat for the best example imaginable of why attachments are forbidden in the form of his best friend’s destruction of everything he knew. It would never happen. Never. He spends the time between episodes 3 and 4 watching over Luke and is a hermit living alone when Luke is in his late teens in 4 so he’d be most likely to have his child soon after he saw what the fear of loss did to his friend, order and galaxy. That in no way matches with anything Obiwan Kenobi has been shown to be.