Do you really know what your kid’s doing on that device?

Yes, Bivens is one of “those moms,” she says. The type who walks into her daughter’s bedroom without knocking; the kind who tightly monitors her daughter’s phone. She makes no apology.

Nor should she, says a retired cybercrimes detective who spoke to her and other parents in early June at Nathan Hale Elementary School in Chicago.

“There is no such thing as privacy for children,” Rich Wistocki told them.

Other tech experts might disagree. But even they worry about the secret digital lives many teens are leading, and the dreadful array of consequences — including harassment and occasional suicides — that can result.

Today’s kids are meeting strangers, some of them adults, on a variety of apps. They range from the seemingly innocuous Musical.ly — which lets users share lip-syncing videos — to WhatsApp and, more recently, Houseparty, a group video chat service. Teens are storing risque photos in disguised vault apps, and then trading those photos like baseball cards.

Some even have secret “burner” phones to avoid parental monitoring, or share passwords with friends who can post on their accounts when privileges are taken away.

David Coffey, a dad and tech expert from Cadillac, Michigan, said he was floored when his two teens told him about some of the sneaky things their peers are doing, even in their small, rural town.