That's often the way, naomi. Breastfeed in front of a 3 year old and they won't bat an eyelid. In front of a 50 year old man, say, and they might be embarrassed, because they have learned to sexualise breasts by then. It's our own fault.
It's about context, anyway. If I posted photos on here of a naked man and woman, say, it would likely be removed for being inappropriate. But the majority of babies, young children, will have (you would hope) already seen both parents naked at some point.
Education and gratification shouldn't be treated as though they are the same.