The youngster's offense? He allegedly rode a dirt bike on a sidewalk.
"They scared me," Gerard Mungo Jr., age 7, told The Baltimore Examiner before breaking down in tears.
"They locked me up on the bench with one hand," he said.
The incident brought new heat on a department already under fire for making what critics call frivolous or unnecessary arrests.
Mayor Sheila Dixon apologized Friday for the arrest.
"It is clear to me that the arrest was wrong, that the officers on the scene should not have arrested the child, and on behalf of the City of Baltimore I apologize to the boy and his parents," she said at a press conference Friday, flanked by the police commissioner.
Police commissioner Leonard Hamm, while noting concern over the nuisance of dirt bikes, said that the arrest of the 7-year-old "was not consistent with my philosophy of trying to solve problems in the neighborhoods" and would be investigated internally.
Gerard's family members say the bike wasn't even running at the time, reports CBS station WJZ-TV. "They yanked me off the dirt bike," Gerard said.
The police commissioner said that the officer had the option of having a conversation with the parent or confiscating the bike. He declined to discuss how the incident unfolded, saying more time was needed to complete the internal investigation.
Dinkins, who turned 7 last month, was sitting on the bike Tuesday with the motor off on a sidewalk near his home in east Baltimore when an officer grabbed him by the collar and pulled him off the bike, according to his mother, Kikisa Dinkins, who witnessed the arrest.
"I told them to let go of my baby," Dinkins recalled. "Since when do you pull a 7-year-old child by his neck and drag him?"
Dinkins said she called for a police supervisor to intervene, but the confrontation continued to escalate after the supervisor arrived on the scene.
"They started yelling at him, 'Do you know what you did wrong, son?"' Dinkins said. "He was so scared he ran upstairs."
Police confiscated the dirt bike and placed her son under arrest.
At the station, young Gerard was handcuffed to a bench and interrogated, before he was released to the custody of his parents, his mother said. Hamm could not confirm that the child was fingerprinted and photographed. He said that would not have been normal procedure in a non-felony case.
The zero-tolerance arrest policy of former Mayor Martin O'Malley, now Maryland's governor, has become a contentious issue in Baltimore, with State's Attorney Patricia Jessamy, some judges and civil rights activists complaining such arrests occur most often in poor, black neighborhoods.
Dixon said Friday that the arrest isn't reflective of her philosophy on policing, and Hamm agreed.
Dinkins said the incident has scarred her son. "This has changed his life," she said. "He'll never be the same."