In the ~5 years we've been doing LANdemonium, we have never had an incident of anyone getting hurt or anything getting stolen.
As Ryan says we have some one there 24/7.
We'll be at the Crowne Plaza in our own room. Once it starts getting late and it looks like everyone is settled in we shut the doors to our room and only people who belong at the lan are allowed in.
If we were to ever find anyone doing something they shouldn't be at the lan, we would eject them immediately.
Like Ryan said, there are a lot worse things out there for a 16 yr old to be doing then playing computer games in a nice hotel with his friends