MomsTeam.com has some excellent information on preventing sexual abuse in youth sports.
From the page: Background Checks A Good First Step:
Coach And Player: Never Alone
There a variety of steps a parent can take to protect their child from sexual predators. By far the most important step is to make sure your child is never alone with the coach by instituting a two-adult rule. Such a rule is good because it:
•Protects the child: A child is vulnerable to sexual abuse by a coach because he or she inherently trusts the coach and may be unable and unwilling to accept an abuse of that trust. If the coach is never alone with a child, the child is protected from being a victim of sexual molestation; and
•Protects the coach: Prohibiting a coach and player from being alone also protects the coach from accusation or innuendo that something could have gone wrong. A coach's career can be destroyed if the accusation of inappropriate behavior is made because the coach has no way of defending himself if he was alone with a child. This is a simple but powerful protection for all people involved. If an opportunity for inappropriate behavior never exists then inappropriate behavior cannot be alleged. Neither is inappropriate behavior likely.
Teaching safe versus unsafe touching
Parents should also be proactive in establishing a safe environment for their kids as well making sure adults act appropriately. Children should be taught how to determine what is safe touch and what is bad touch. In youth sports, touching does occur. But it is imperative that the child feels comfortable with the type of touch that is appropriate in sports and can determine if a coach or player has stepped over that line into inappropriate touching.