Rape, no, consensual sex, behind closed doors, in the bedroom. And we have already agreed not to be bothered about what's going behind closed doors.
And if you don't know the basics, legal age of a person who can give consent to sex varies in countries. Your definition of child might very well mean adult in some other country.
It's not objectively possible to lay down a perfect law. If it can ensure that a good number of people are protected then it is better than no law at all. There will be exceptional cases, no denying that. I am pretty sure that you understand the concept of "works in most scenarios barring few exceptions".
If you don't know how legalizing same sex marriage will help towards equal laws then I will leave the matter here.
Out of this thread because you are just feeding off of the minor points to feel good about your opinions.