The key to a satisfying mother son relationship (as well as opportunity) is "early grooming" - while still in single digit age, be not so guarded about your body, loose fit clothes with no bra or panties, let him see your body but not "in ya face" full display, nudity has to remain sexual. In the video the mother was cool to not freak out over her son's porn magazines and then to invite him to join her in the bath and let him soap her naked body - and let him fuck her from behind and then masturbate him to cum on her tits - it's all very calm and related and perfectly natural between mother and son while Dad is away at work.