FRANKFORT, Ky. — Kentucky’s highest court considered on Thursday whether teen-age couples should be treated as criminals when they have sex and send nude photos to each other. If so, a third of America’s teenagers could be exposed to felony sex-offense charges, the 15-year-old boy’s lawyer said.

In this case, the legal fallout was one-sided after a mother spotted nude pictures on her seventh-grade daughter’s phone, and discovered that she was having sex with her eighth-grade boyfriend at her house.

Both teen-agers could have been charged with the same offenses, but the full weight of Kentucky’s law landed on the boy, who pleaded guilty to two misdemeanors for having sex and exchanging the photos. Then, despite his plea, a judge designated him a sex offender, removed him from his home and sent him to a juvenile detention center.

Lawyers for the boy and the Commonwealth of Kentucky argued for nearly an hour before the state Supreme Court over whether this kind of voluntary sexual conduct between children should be criminalized at all.

“They had no idea they could be committing crimes,” said assistant public advocate John Wampler, who represents the boy.

Laws in Kentucky and many other states establish that no one under 16 can legally consent to sex. This boy was 15 and his girlfriend was 13 when they twice had sex.

The state’s high court is expected to issue a ruling within a few months.