Yes, there has to be a natural element to it, to some extent in as much as the urge to have physical/sexual contact is something that presumably exists within those people - I suppose its a nature vs nurture debate (ie for nurture, what they see and may have experienced themselves) as to how they get those urges but at the end of the day, they feel what they feel and they want to act on it. Its a bodily reaction - if they didn't feel attracted to children in the first place then it would never happen in the first place surely?.
ETA - perhaps biological is a better term to use than natural as such? just a thought.
It's very hard to tell where it comes from Izzy and how much nature or nurture it comes from. But it seems to be widespread across all cultures and has been around for centuries suggesting that it seems to be an inherent part of human sexuality and is probably a sexual orientation in itself.
That doesn't mean anyone wants to see it legalised or normalised though. I don't see any benefit for children to have adults sexually interested in them. But accepting that it is a part of human sexuality might make society more tolerant and understanding when trying to deal with those with that inclination.