Let's be clear on the underlying assumption of this question: in and of themselves, the acts are never wrong.
Instead, acts are wrong or not, based on the context in which they're performed.
In other words, it's moral relativism.
Perhaps a better question might be: "is there any action that is intrinsically wrong?"
You've hit the nail on the head - why is pedophilia wrong if homosexuality is right - particularly if 'informed consent' and be demonstrated in both? I always get "the difference is obvious" argument but no one explains why it's so obvious. From my perspective it's obvious why homosexuality is wrong but when I offer up my reasons they are discounted because they are a) religious in nature, b) suspect in their origins, c) refuted by other studies that demonstrate my studies just wrong because their study supports their point of view and mine's just obviously wrong.
Good question. Males and females are intrinsically structured such that the males sex organs fit the female sex organs. The sex organs are apparently for procreation.
Pre-pubescent children do not have the capability to have children. So some of this depends on what a "child" is. It's not uncommon to call a 14 year-old a child but physically two 14 year-olds to could make babies. But so could a 14 year-old and a 25 year-old.
I would start from a design perspective and look at how our bodies are designed. Then we factor in other conserations, like societal concerns and come up with an age everyone can agree is a good age for people to start making desicions about sex. We legislate morality by concensus by saying that adults cannot have sex with minors.
Both homosexuality and pedophilia are perversions and immoral based on a religious basis. We don't have to be ashamed of that. For if the homosexual activists wish to assert some sort of absolute claim to morality, that homosexuality is moral, they must borrow from some objective moral law giver. Of course, that a whole 'nuther topic.