Do you know how easy it is to fake AIM records, especially chat transcripts? I could create an AIM conversation between the two of us talking about flying red donkeys and it would look authentic and it would take me about 10 seconds. ABC does not have the legal authority to get access to anything on AOL's end either, so there's absolutely no proof of what they say. I'm not sure if even the FBI could get this kind of log because I'm not sure what records of AIM conversations are kept by AOL for long periods of time.
The bottom line in my mind is whether the guy solicited the kids for sex. That would be illegal. Telling them a dirty joke most likely would not be, but I admit that would be of questionable morality.