Three Tredyffrin/Easttown district students face charges of distributing or offering to share sexually explicit images - including photos of their middle-school classmates - after an investigation that police say could expand to implicate more children.

The students, ages 11 to 15, were not identified. They face juvenile charges as well as disciplinary action by the district, routinely ranked among the state's best public school systems.

Victims and participants told investigators that images of child erotica, nudity, child pornography, and pornography had been created, sent, stored, and viewed by students at their homes and in school over the last six months, Tredyffrin Township police said. The students attended Valley Forge and Tredyffrin/Easttown middle schools.

In one incident, a student allegedly offered to sell an explicit image of a classmate to another student. In another, police say, a student took an image of a sex act from the Internet and distributed it to classmates, saying it featured a female student in their schools.

"Incidents such as these are greatly concerning, especially due to its impact on young victims and their families," Police Superintendent Anthony Giaimo said in a statement Tuesday, a day after the charges were filed. "We urge parents to take a very active role in monitoring Internet and cell usage on the part of their children."

The criminal counts include transmission of sexually explicit images by a minor and criminal use of a communications facility. The cases will be adjudicated in Juvenile Court.

Police would not say how many students were involved in sexting, nor would they say how the investigation started. At least one of the three charged entered high school this fall, according to Sgt. Todd Bereda, spokesman for Tredyffrin police. The investigation is ongoing, and more students could be charged, he said.

"We take these matters very seriously and follow up with procedures that promote safety for all students," Mark Cataldi, the school district's safety coordinator, said in a statement posted Tuesday on its website. "We join with the police and the entire community to emphasize responsible use of technology and to affirm the rights of all individuals to live and thrive in an environment free from harassment."

In 2009, the Pew Internet and American Life project reported that 15 percent of cellphone owning teens ages 12 to 17 had received sexually suggestive nude or nearly nude images via text message.

As sexting became more common, some states initially charged juveniles under child pornography laws, drawing criticism for being too harsh. But even new laws specifically designed for children who offend have been controversial, including one passed in Pennsylvania in 2012.

That law made it a summary offense for a minor to send an explicit photo of himself or herself and a misdemeanor if the image is of someone else. The statute also requires a judge at sentencing to first consider a diversion program, which would be followed by expunging of the charge from the child's record.

In response, the Philadelphia-based Juvenile Law Center claimed the law was "ill-suited to addressing adolescent behaviors."

"Children need education and guidance from parents for their reckless, immature, and often stupid behavior," the center said in 2012. "Prosecutors and other members of law enforcement should direct their attention to real criminal activity."

Speaking about the issue in general, JLC lawyer Riya Shah said law enforcement can be too quick to criminalize such behavior.

"When you put these devices in kids' hands without the proper education in how to use them, the response shouldn't be to lock them up if they do something wrong with them," she said.

But Barbara Ashcroft, a Temple University law professor and former chief of the Montgomery County District Attorney's Office's sex crimes unit, said she would have filed the charges in Chester County. She said Pennsylvania law and the juvenile justice system are designed to hear the child's side of the case and provide counseling and other rehabilitative resources.

"I think it has to be on a case-by-case basis," she said, "but if you don't provide for consequences, a lot of harm can be created through the unbridled discretion that these kids have with their cellphones."

Many of the children in the Tredyffrin case took images of themselves at home with the location settings activated on their phones, Bereda said. That means people who view the images, including child predators, would be able to determine where they live.

One of the parents routinely checked his son's cellphone and computer use, police said, so the son stored and retrieved intimate images using a cloud-based storage service that was hidden from his parents.

Ashcroft, the Temple professor, called sexting and the sharing of images among teens "an epidemic which requires more education in our schools and at home to protect these kids from their hormones and cellphones."

610-313-8207 @MichaelleBond