Twenty-one people have been charged with sexually exploiting children online, New Jersey Attorney General Gurbir S. Grewal said Wednesday as he and other authorities announced their arrests and urged parents to actively monitor their children’s cellphone, gaming, and internet activities.

Nineteen men, one woman, and a 15-year-old boy were arrested in “Operation Screen Capture,” a statewide effort launched in March — at the start of the coronavirus pandemic — in response to an alarming increase in potential threats to children from online predators, authorities said.

“Homebound children are spending more time on their devices, both for virtual learning and for recreation,” Grewal said during a virtual news conference. “And at the same time, predators are also spending more time online, taking advantage of this situation.

“Apps and gaming systems continue to be prime hunting grounds for child predators seeking victims,” he said.

Three of the defendants — Aaron Craiger, 34, of Oklahoma, who authorities say traveled to an Atlantic City motel to meet two men who offered him access to underage girls for sex; Jason Berry, 40, of Monmouth County; and Alize Tejada, 21, a babysitter in Newark — were charged with attempted sexual assault or sexual assault and child-pornography offenses.

The 18 other defendants were charged with endangering the welfare of children for possession or distribution of child sexual-abuse materials, including, in many cases, videos of sex acts involving children, authorities said. They include Kevin Carrierri, 34, of Toms River; Christopher Crispino, 45, of Bellmawr; Shawn Daily, 45, of Browns Mills; Roy Dantz, 71, of Mount Laurel; Brett Warfield, 21, of Carneys Point; Henry Ziolkowski, 66, of Toms River; and a 15-year-old boy from Gloucester County.

With many schools beginning virtually this fall, Grewal urged parents to teach children that the people they encounter online might not be who they seem to be; to familiarize themselves with the apps and games their children are playing; to check the security settings on their cellphones and other devices; to remind children not to share their personal information or take inappropriate photos or videos of themselves. He also said parents should be wary if their children are being secretive.

The New Jersey State Police, U.S. Homeland Security Investigations, and county prosecutors worked with the Attorney General’s Office on the case. Authorities asked anyone suspecting child sexual exploitation to contact the National Center for Missing & Exploited Children at 800-843-5678 or online at report.cybertip.org.