Two Brooklyn moms took “tough love” to a new level Friday, turning their teenage daughters in to the cops after one recognized them in a wanted photo in the beating of a 78-year-old straphanger.

The girls, ages 15 and 16, had allegedly pounded Nora Trotman on a Bedford-Stuyvesant subway platform the previous day — because she had asked the girls to remove their feet from a seat on a Manhattan-bound C train, police said.

“Shut the f–k up!” the older girl, Jazmine Watson, snarled as detectives walked her out of the transit precinct in ­Coney Island.

Thanks to their moms’ detective work, Watson is now charged as an adult with felony assault, and her younger pal is charged with assault as a juvenile.

The two moms “were probably offended like anyone else” who heard about the senseless attack, one law-enforcement source said.

“And when they recognized their daughters, they were probably appalled.”

The senior citizen had been on the same train as the two girls and their friends at about 3:30 p.m. Thursday, and had asked one of them to remove her feet from a seat so she could sit down, police said. But instead of complying politely, the two followed her as she exited the train at the Franklin Avenue station.

They allegedly attacked Trotman, punching and kicking her multiple times, including in the head and face.

They then escaped by boarding another train — but not before their images were captured on surveillance video.

Trotman, who family said had been going to her physical therapist, was rushed to the hospital. She was treated for cuts and bruises and released.

Cops quickly publicized ­photos of the two attackers. And on Friday, the mom of the 16-year-old marched her daughter into the 75th Precinct station house in East New York, and the mom of the 15-year-old dragged her daughter to the 79th Precinct station house in Bedford-Stuyvesant.

By Friday afternoon, Trotman was well enough to aid police in the investigation.

She and her daughter were picked up by Transit Bureau detectives and driven to Transit District 34, where she identified the two girls in a lineup, according to sources.

By 6 p.m., Trotman was driven back home.

“She’s a loving woman, very caring and a very loving grandmother,” her son, Owen, told The Post.

“I don’t know what the world is coming to,” said neighbor Gregory Goins, 64.

A high-placed police source said the two mothers should serve as an example. “More parents, if their children do wrong, need to step up like these mothers did,’’ he said.

Additional reporting by Amanda Woods, Matthew ­Allan, Megan McGibney, Abigail Gepner and Shawn Cohen