Some help with a difficult dilemma dealing with a mentally handicapped adult.?

My brother is 19 years old and mentally handicapped, but not severely. He can do a lot of things for himself, but his mentality is that of a 9 year old boy. However he seems to have the normal ual needs of a boy his age, without the common sense/intelligence to know whats right and wrong. Recently we've been having issues with him peeking in on my 13 year old sisters friends getting dressed, and things like that, so she's had to put a lock on her door and no longer has friends over at night. Now this worried my family, and has caused a lot of family tension, but not like what I found last week. Last week my mother was complaining about her computer having a lot of issues so I got on it to clean it out. Being snoopy and the adult sister, I figured I'd snoop on what my sister and brother had been up to for my mother. While looking through the history I found a lot of animated which had obviously been looked at by my brother. Now the problem is what it was of, a lot of it was over children, some of them very small and this has our whole family in an uproar and choosing sides. My other adult sister and I both have children of our own, some around the same ages as the girls depicted, so we no longer feel comfortable having our brother around and have had to talk to our girls about things we wish we hadn't. However we're all pretty sure that nothing has happened, although both of us are worried about adding a yet to the end of that sentence. My mother says that it's not real and is both scared for her grandchildren and defensive of her son, it has her very confused and lost. I live in the florida area and mainly I was wondering, is there help for this sort of thing? Like a hotline or a place we can look at sending him for a bit that will help us deal with this situation before my mentally handicapped brother becomes a pedophile, or should we just take a step back and be careful and not allow him to be alone with any of the children. I've been searching all over google and can't find a single thing on this sort of stuff, so mainly I'm looking for resources for my family.