Editor's note: Find more resources on how to deal with child abuse on "Stop It Now."
(CNN) -- The teen's mother began to suspect something was wrong a few weeks before her son told a school principal that former Penn State football coach Jerry Sandusky had molested him.
He'd begun to act out, the woman told the Patriot-News, and ask her about a database for "sex weirdos."
The boy's report led to a three-year investigation, culminating in charges against Sandusky related to eight alleged victims.
The young man, identified in court papers as victim 1, accused Sandusky of four years of abuse that started after a graduate assistant reported seeing Sandusky sexually assaulting a young boy in a shower in 2002. Prosecutors allege administrators ignored the report and that their inaction allowed the pattern of abuse to continue.
If the allegations prove true, it would underscore an unfortunate reality in many child sex abuse cases: that signs were missed, overlooked or ignored.
Most children are abused by someone they know and trust, according to the American Psychological Association. An estimated 60% of perpetrators are known to the child but not family members: family friends, babysitters, child care providers and neighbors.
"The real tragedy here is that many people within the organization may have known of this activity, either because of reports or through witnessing it, and didn't carry it further," said R. Daryl Steiner, director of Child Protection and Child Abuse Prevention at Akron Children's Hospital in Ohio.
Vigilant parenting is the first line of defense in preventing abuse, experts say. Several spoke with CNN about how parents should talk to children, how to identify potential abusers and how to recognize the red flags that should lead to further investigation.
Establish an open relationship with your child
An important part of preventing abuse is letting children know they can tell you absolutely anything without worrying about getting in trouble, said psychologist Elizabeth Lombardo, author of "A Happy You: Your Ultimate Prescription for Happiness."
An open relationship fosters trust. That means children are more likely to pay attention when you tell them never to be alone with an adult, or the difference between a good touch and a bad touch.
Be present, be aware
Parents often let their guard down and forget the basics, said Steiner.
Be aware of where your children are and who they're with. Make sure they're never alone with adults in an isolated setting and show up for their activities when you can. That doesn't mean attend every single baseball practice, but be present enough to know what's going on and to ensure your child is never alone with an adult.
"It seems like common sense because it is. But just knowing what your children are doing and being involved in their lives, not only with general knowledge but with your physical presence, allows you to monitor the situation. It also established you as a parent who's active in your child's life, which makes you an obstacle for someone trying to groom your child for abuse."
When choosing an organization or program for your child, make sure it has a policy against children being alone with a single adult, he said. Make sure the atmosphere is open and transparent in the literal sense -- no closed doors or private sessions, and parents should always be able to sit in on activities.
Learn to recognize risky behavior in adults
Identifying risky behavior in adults with whom you leave your children helps prevent abuse, said Sharon Doty, a child abuse prevention expert and founder of the nonprofit organization Empowering Adults -- Protecting Children.
- People who want to be alone with children: If a predator has nurtured a relationship, you may be inclined to let him or her be alone with your child if the adult asks. But just say no, Doty said.
- People who break the parents' rules: Be wary of people who give your children candy or food against your wishes or let your child do things you don't allow them to do. "It creates a secret relationship. You have to be advocate for no secrets by teaching that it's never OK for someone to ask them to keep something from a parent," Doty said.
How are you supposed to know what's going on behind your back?
"If you listen, you'll often find out. Listen to them talk to other kids, listen to their car talk while you're driving. Notice if the child has become wary of talking to you. Observe situational and behavioral changes."
Recognize warning signs in your child
Young victims of abuse tend to adopt unusual behaviors to escape their torment as a means of coping, Steiner said. They may start dressing shabbily to make themselves less attractive or appealing to their abuser. Children also tend to withdraw or isolate themselves out of shame.
"They're trying to escape the abuse, the tragedy and harm they feel, and they don't know how to do it, so they try to change the circumstances of their lives," he said.
Other warning signs could be new symptoms of depression and anxiety, poor performance in school or disinterest in activities they used to enjoy, Lombardo said. Don't be dismissive if a child no longer wants to go to soccer practice or expresses a sudden dislike for a coach or teacher. Take it seriously and find out why.
Teenagers might also act out with substance abuse as a means of coping, she said.
"In general, we tend to not compartmentalize stress very well. Because abuse is so distressing and upsetting for kids, they don't know what to do with the stress, so they act out in other ways," she said.
Other signs run the gamut from mood swings and changes in eating habits to more overt clues involving adult-like sexual behaviors.
Don't be afraid to talk to your child
It's hard to ask your child about what's going on in his or her life, especially when abuse is suspected. The key is to do it in a nonconfrontational manner that doesn't convey anger, distress or concern; you're the adult and caregiver, after all, and you set the tone, Lombardo said. Don't have the discussion before school or at bedtime; pick a moment when you have time to talk freely, without time constraints.
Parents should test different conversation openers in advance to find one they're comfortable with, said Doty, the child abuse prevention expert.
Maybe something along the lines of, "Once upon a time, something happened to me and it took me a long time to tell someone, but I felt much better once I did," she suggested. Or, "What's the best thing about coach so-and-so; what's the worst thing?"
"Even if they don't tell you straight up, they might give you hints of things that concern you. Listen to your gut," she said.