Exclusive Type: Adults only sexually attracted to children.
Non-Exclusive Type: Adults are sexually attracted to male/female child and also adults.

 WHAT RESEARCH SAY:

 There is some evidence that pedophilia may run in families, but it hasn't been 100 percent proven
 Other factors including, abnormalities in male sexual hormones or the brain chemical "serotonin". Again, this has been hypothesized, and hasn't been totally proven.
Twenty years ago or so, it was believed that children who were sexually abused, grew up to be abusers themselves. Nowadays, research has proven that there is no evidence that children who are abused are more likely to sexually abuse a child later in life.

 When I was younger, I had a real close friend, who was always with me. We were best friends, and we were always together. Eventually he moved away, and I never seen him since. The reason I say this is because I think many pedophiles had similiar experiences or had sexual relationships with other kids during their childhood. As I was growing up, I missed my childhood friend a lot. I think(and I could be wrong) that I started seeking other boys out, thinking I would find another boy just like him. I believe over time, the thought process of finding a child becomes conditioned in ones brain(seeking love, comfort) from past experiences. As the individual becomes older, there still seeking out their first "attraction", which consequently will be a child, since their first love has grown up as well. Sexual attraction is embedded within the conditioning in ones sub-concious mind.
Again what I wrote above is just my personal view, meaning there probably isn't research out their to support this.