What are the limits of 'awrah (intimate parts) and what can be revealed of the body in front of a four-year-old son? And is it permissible to let him touch his mother's body or look at it while she is changing clothes, especially if he is curious to know the differences between a girl and a boy?

It is permissible for a mother to expose before her four-year-old child what she would conceal from discerning children, because he generally does not distinguish between 'awrah (intimate parts) and other parts, nor does he comprehend these matters. The Hanbalis held that it is not obligatory to cover oneself from a non-discerning child. The Shafi'is differentiated the viewing of a child into three degrees: The first is that he is not old enough to narrate what he sees; his presence is like his absence, and it is permissible to uncover oneself before him. The second is that he is old enough to narrate what he sees, but there is no arousal of lust; in this case, it is permissible for a woman to expose before him what she exposes before her maharim (unmarriageable kin). The third is that he is old enough to narrate what he sees and there is arousal of lust; this child is then like an adult.