Three boys around the age of 12 have been arrested in Sydney's inner city after a 10-year-old boy is stabbed in the torso.

Police were called to John Street, Waterloo about 12:15pm following reports of an assault.

They found the 10-year-old with a laceration to his torso and he was treated by paramedics before being taken to Prince of Wales Children's Hospital in a stable condition.

The three boys who were arrested at the scene are assisting with inquiries at Redfern Police Station.