Good advice yes. But since when does this fine JWD forum believe that living a lie is the best route, because someone may be temporarily upset by facts.
It may be unfair for the child (sound like he's grown by now) to not know the truth. There is a slim possibility of medical problems that could require the truth of his father's identity, like if he needs a transplant, or needs to know family history esp if his real father is dead and at what age.
I guess I would say that TRUTH and HONESTY are everything, without them, we have nothing.