A teenage boy attacked a couple and threatened their 10-month-old child with a rock in Phillip on Wednesday night, police say.

Police said they had questioned a 14-year-old boy over the robbery, in which a 34-year-old man was hit in the face with the rock and had money taken from him.

"Around 7pm a couple from Lyons went for a walk to the Chifley shops with their 10-month old child in a pram," police said in a statement.

"As they walked from beneath the pedestrian underpass on Hindmarsh Drive, they were approached from behind by a boy who held a rock in his hand, menaced the couple with the rock, and demanded money from the couple.

"The boy then struck the 34-year-old male victim on the face with the rock, and threatened the woman and her child. The victim then surrendered a small sum of cash, and the offender fled back into the underpass in the direction of Lyons."

The boy was described as fair-skinned, with a thin build, 165­—168cm (5’5” to 5’6”) tall and wearing a T-shirt and shorts.

"A short time later, police located a 14-year-old boy whose appearance was similar to the description provided. The boy was questioned, details were taken, and he was released into the care of a responsible adult pending further police enquiries," police said.

Police ask anyone who knows anything about the incident to contact Crime Stoppers on 1800 333 000 or atwww.act.crimestoppers.com.au.

canberratimes.com.au