There's something to be said, within a family, for not making a very big deal about anatomy and nudity, though its also important ( as the child will have through life to interact with other people with different attitudes, to foster a sensible sense of privacy and modesty, too. There are no necessary ill-effects, but much depends on other elements of the relationships, and some mothers are unwholesomely seductive towards their sons --- and at early adolescence this could be bothersome and confusing for the lad