The reason that the 2 witness rules is so messed up is that no child molestor is dumb enough to let anyone witness their crime. The only witness is the victim! So unless the perp is molesting more than one kid at a time or gets caught literally with his pants down, he's immune to prosecution!
In my congregation this is actually what happened to a brother. His wife caught him doing something with their daughter. If I knew who he was I might turn him in myself, but this is just something my mom picked up from the JW rumor mill.
While it's true that kids do lie like everyone else, there are actually fairly reliable methods of determining guilt. Just run the kid's clothing or bed sheets over with a black light. Is there semen? Does its DNA match that of the accused? Case closed.
The reason the two witness rule exists is because the GB knows it doesn't work. They don't want it to be known that their 'clean' organization is crawling with pedos, so they have deliberately made it as difficult as possible to 'convict' them. Once you have recognized this, everything makes sense.