@jaketheripper, in addition to what @rasputin6xc said, I also don’t really understand what objective morality you would invoke to “prove” that child rape was objectively bad.
The Bible, for example, allows child rape, provided the child in question is not already sold (i.e. betrothed) to another man to be his future wife. Muhammad married a 9 year old girl, and according to Islam, women are not required to consent to sex.
Opposition to rape is actually a relatively new concept in history that emerged from rational, utilitarian moral values. Hell, it wasn’t even until the 1970’s that the United States courts held that raping one’s wife was legally possible.
This doesn’t mean that rape is “just as wrong or right” as your choice of ice cream, but it does mean that morals evolve over time. But, being rational creatures, we can often get a good idea of what morals seem to “work” for our species, and which ones don’t.