Yes, good question.
We've just had a few cases of famous pedophiles tried in France and from the little explaining that specialists gave on television, it may be the case that the attraction they feel to children started with something specific in their childhood. They will associate a specific age in a "partner" with intense happiness. It seems to me that they are mentally disturbed and not necessarily responsible for this urge they feel.
The next question then is: are they responsible for turning the urge into action? In most cases, definitely yes! I always think it's a joke when I hear of the state providing compulsory psychiatric treatment for those people. Most of them have no interest in being cured, and a lot of interest in further gratification of their pleasure.
What they do is particularly shocking because it happens to children, but it is the same principle that rules all criminal life, and a lot of actions that are never recognized as offences. I call it "I see, I want, I grab".
It may end up in theft, in business fraud, in rape. The idea is: this action is pleasurable to me, and I shall not deny myself the satisfaction of taking what I crave.
What they all have in common is lack of empathy, the inability to share the victim's suffering-- but then with criminals, this is nothing new.
The only reason the thief is better than the pedophile is that he has no interest in young children (not that he is a better person), and a lot of interest in material goods. Apart from this, they follow the same logic.