"Behavior like this can't keep going on and on," said Andrea DiFonzo, a Northeast Philadelphia mom who says her high school daughter is a victim of bullying on Snapchat, a popular messaging and photo-sharing app where posts are meant to disappear after they're viewed.

"When this happens, kids see these images online or hear these again and again and again, so it's like they're being repeatedly traumatized," said Dr. Stephen Leff, a child psychologist and co-director for the Center for Violence Prevention at Children's Hospital of Philadelphia.

He says it's important parents look out for signs their kids are being bullied, like headaches, stomach aches, and children getting upset while playing a game online.

"The fact that they're home more and have less access to friends makes it even worse, and that's why I think it's really important as parents that we open lines of communication, and ask our kids how their days are going," he said.