Four boys were arrested on suspicion of GBH after a man in his 30s was beaten up in a Mare Street shop.
Police were called at 11.40pm on Thursday night and detained two 15-year-olds, a 14-year-old and a 13-year-old in nearby Richmond Road.
The victim was taken to hospital with an eye injury. Scotland Yard said his condition was not life-threatening.
All four boys have been bailed.
Officers are still investigating what happened.
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