A group of teenagers assaulted and robbed another group of teenagers riding the Expo Line from downtown Santa Monica to Culver City Friday evening.

A group of five Culver City High School students between 14 and 17 years old boarded the Expo Line in Downtown Santa Monica after visiting the local beach. A group of about 15 teenagers boarded the train with them and the two groups began talking and dancing together. When the high schoolers got off the train at the Culver City station, the larger group followed them. They allegedly attacked the five students and stole their belongings, said Noelle Hannemann, the mother of two of the students.

The Culver City Police Department confirmed that a group of 15 teenagers jumped and robbed a group of five other teenagers around 10:20 p.m. Aug. 2. Officers took three teenagers into custody as suspects in the robbery, said CCPD spokesperson Marissa Yabko.

Hannemann said when her sons arrived at the downtown Santa Monica platform with their three friends, a group of teenagers asked them if they were members of a gang. Her sons said they were not and both groups entered the train, where they started playing music and talking.

“They were really nice,” Hannemann said. “But they kept asking where they were getting off, and then one of them started looking through my son’s backpack.”

Both groups got off the train at the Culver City station. The larger group followed the five teenagers down the stairs and one punched Hannemann’s 14-year-old son in the jaw and head, she said. Her 16-year-old son intervened and was punched in the head and kicked in the ribs and head.

Their three friends — a 17-year-old boy, his 15-year-old sister and another 15-year-old girl — were also attacked, Hannemann said.

She said the group of teenagers took their phones, shoes, a backpack and a pair of headphones.

Hannemann’s older son called her immediately after they were attacked and she drove to the Culver City station within 10 minutes, she said.

Her 14-year-old son was taken to Cedars-Sinai Marina Del Rey Hospital, where doctors determined that his jaw was broken in two places and a CT scan indicated that he might have suffered a small brain hemorrhage.

He was transported to Cedars-Sinai in Los Angeles by ambulance around 5 a.m. Saturday morning, Hannemann said. A second CT scan found no evidence of internal bleeding, she said.

One girl suffered a broken nose. Hannemann’s older son and the other two teenagers sustained bruises and other minor injuries but were not hospitalized.

“We’re really lucky that it wasn’t worse and we’re really counting our blessings,” she said.

She added she will no longer allow her children to ride the Expo Line at night.

This article was updated Aug. 7 at 11:08 a.m.

madeleine@smdp.com