A man, apparently irritated by a crying child, pushed the 3-year-old boy to the ground, then punched his mother when she came to his aid, Takoma Park police said.
They said it happened about 11:30 a.m. Friday as the woman and her son were at a bus stop in the 7600 block of New Hampshire Avenue.
The police said they were told that the man ordered the woman to “shut her kid up.”
When the child continued to cry, police said, the man pushed his head, knocking him down.
The woman attempted to defend her son, the police said, but was struck in the mouth.
Neither was seriously injured, police said.
The site of the incident is about a quarter-mile south of East University Boulevard and near two shopping centers. It was not clear how many people witnessed the incident.
Police said the man fled, heading south on New Hampshire. He was described as black, about 5 feet 5 inches and 150 pounds, with short twists in his hair.
Police said they searched but did not find him.
They notified nearby jurisdictions and asked anyone with information to call them at 301-270-1100.