Prince George's County police have launched an investigation at Stephen Decatur Middle School after three adults assaulted and injured a 14-year-old boy Wednesday.

Police said the trouble started after a 13-year-old boy and the 14-year-old were sent to the principal's office at the school in Clinton after the two fought during lunch. School officials called relatives of the boys, who were not identified because of their age, to come to the school to pick them up.

The mother of the 13-year-old arrived at the principal's office with two other adults about 2:30 p.m., according to police and school officials. As they were leaving the building, the mother of the 13-year-old shouted at the 14-year-old when she saw him through the window of a school office. Then a man who was with the mother of the 13-year-old struck the 14-year-old, police said, and the confrontation escalated. School officials intervened and called police as the three adults and the 13-year-old fled the school campus.

Police Cpl. Stephen Pacheco said investigators are working to identify the adults involved in the assault, but they are believed to be relatives of the 13-year-old.

John White, a spokesman for county schools, said it was unclear what started the fight between the two seventh-grade boys, adding that he did not know how many blows were exchanged in the assault on the 14-year-old by the adults or the nature of the boy's injuries.

"I don't have any details on the injuries, but obviously if the staff hadn't jumped in it would have been more serious," White said.

The boys could face suspension for fighting, White said.

Pacheco said the investigation into the actions of the adults is ongoing.

"The adults were the culprits in this situation," Pacheco said.