This was asked somewhere a few weeks ago. The problem #1 Background checks are expensive.
#2 we interview and have auditions to weed out anyone we feel can no meet our expectations.
#3 Out of 50 actors we might hire 2 or 3 under 18. At least the 18+ are legal adults....
And having key leaders that report any "misconduct" is always a big help (Or as we call them $1 more an hour spies...)