We have two distinct scenes involving fathers and sons: Siddhartha and his father and Siddhartha and his son. In both, the son wants to leave, and in both, the father indulges and is hurt by it. So maybe the suggestion is that fathers must let go of their sons to find their own way in the world, even against their own better judgement. Perhaps this means that fathers and sons cannot truly connect.
There's also a sharp difference between these two instances. Siddhartha is respectful of his father and wishes his blessings, even if he rejects what his father wants. His own son, however, is bratty and disrespectful. But like his own Brahman father, Siddhartha indulges his son. There's a parallel in that the way our parents treat us is the way we will treat our own children.
There is definite tension between Siddhartha and his own father, or he would not have felt discontent and left the fold of his cushy life in the first place.
Siddhartha finds a father figure in the ferryman, and stays there for quite some time.
His own son and he do not ever truly get along...
Seems as if Hesse is sending us a message to have girl-children only. Ha!