(CNN) -- It's hard to pin down the numbers. The American Academy of Child & Adolescent Psychiatry says child sex abuse is reported 80,000 times a year. But experts acknowledge those numbers are just a drop in the bucket. Many more child sex abuse cases never go reported.
"Most of the kids don't report that someone did something to them; there's the whole shame factor," said Steven Lancaster, executive director of the nonprofit Childhelp Alice C. Tyler Village, a residential treatment center for abused children in Lignum, Virginia.
Lancaster said children often won't disclose abuse because they fear they won't be believed or they are afraid of their abuser. He said sexual predators will go to great lengths to cover their actions, including threatening the child.
"It could be everything from convincing a child that no one is going to believe them, you're going to lose friends, everyone is going to hate you, to as drastic as if you tell I'm going to do something horrible to your family," Lancaster said.
Abusers often look for children who are easy targets. It might be a child seeking a parental figure or it could be a child suffering from low self-esteem.
Lancaster said abusers usually do not target the popular child. More often than not, it's the loner in a group.
"If they walked into a room they could pick out which kids they could probably groom and victimize," he said.
Mark Horner, a Virginia clinical psychologist, also works with abused children at the Childhelp center.
He said former Penn State assistant coach Jerry Sandusky's organization Second Mile gave him easy access to at-risk youths. "Instead of having to troll and look for children, they came to him."
"That's a typical process of grooming, becoming a best friend, a caregiver, and tantalizing them -- 'I'm going to take care of you,'" Horner said.
When it's an authority figure or someone who is a pillar in the community, the abuse can go uncovered for years, according to psychologists.
"Our culture wants to believe the best about people, especially admired sports figures or priests," Horner said. "We want to believe the best about people, we idealize them. It makes it that much easier to discount any evidence this person's character has a darker side."
Role for parents
The American Academy of Child and Adolescent Psychiatry advises parents to talk to their children about proper boundaries, starting when they're young.
Children need to be taught that if someone tries to touch them and makes them feel uncomfortable, they should tell them no and report it to a parent right away.
And parents should keep an eye out for unusual behavior.
Children who have been sexually abused may become depressed or withdrawn. They may emotionally regress, with actions such as bed-wetting. They may suddenly not want to go over to someone's house or want to skip a sports practice.
"The main thing is (to) listen carefully and believe what your child is telling you and to inquire if you see your child acting differently," Horner said.
Lisa Sylvester is a CNN correspondent and blogger at ParentsDesk.com. She's on Twitter @LSylvesterCNN. Bethany Swain is a CNN Photojournalist and an adjunct University of Maryland professor. She's on Twitter @BethanySwainCNN.