Carnal is an adjective meaning "of the flesh." This makes carnal relations a subject that kids want to know more about, but one that both kids and parents may be embarrassed to talk about with each other.
Carnal can be used to refer literally to flesh: after lions are done feasting on a downed zebra, vultures might pick over its carnal remains. Another use for carnal is to describe something that is worldly (as opposed to spiritual) — "He didn't have much use for religion, preferring to spend his time on more carnal pursuits."