While adult sex with teenage girls is hardly abnormal in an anthropological sense and doesn’t even seem to violate Natural Law, I still don’t think adults molesting little children is normal, as most tribes and even older societies came out against it. There was a ton of teen sex going on in Rome, but they very much frowned on fucking little kids. Check out Suetonious on that.
There are a few societies like the Samia who do this as a manhood ritual, and the boys are not harmed, but that is more of a cultural ritual than a sexual thing per se.
There are also a few cultures that allow teenage boys to engage in sex with girls their own age and even little girls. I assume the girls are not harmed. In the literature, there was one case of a man in this culture who who was doing sexual things with these little girls too. They didn’t really sanction him other than social isolation and mockery. He was seen as “acting childish, acting like a kid, acting immature, not acting his age,” that sort of thing, but it was not seen as criminal. They simply ridiculed and made fun of him.
Considering that in general, societies across the board seem to frown on adults molesting children, I think I can make a case that child molestation violates the Catholic concept of Natural Law. I think we could say that incest also violates Natural Law and most every society encountered has had an incest taboo.
We can’t say scientifically that these things are morally wrong, but I think we can say that according to Natural Law, they are inherently immoral or wrong, and we can’t say that about a lot of crimes because they are more contingent.
Of course, homosexuality also seems to violate natural day not to mention trannyism. That doesn’t mean that homosexuality is morally wrong, but I think it means that Nature frowns on it and may punish those who take it up. Similarly, Nature very much frowns on trannyism, which once again is more idiotic than immoral, and hence trannies are punished by being miserable, having high suicide rates, etc.