Two 12-year-old boys have been charged with starting a fire Tuesday night in an abandoned Troy Hill home, police said.

The parents of the boys turned them over to police. Both face charges of arson, risking a catastrophe, criminal mischief and conspiracy, according to police spokeswoman Diane Richard.

The fire began in the second floor of a house in the 1400 block of Gardner Street shortly before 8 p.m. Tuesday. Witnesses told police that six to eight children were gathered in front of the house at the time.

Firefighters extinguished the blaze, and there were no injuries. Investigators determined that someone had ignited a mattress inside.

The boys, whose names were not released, were in custody but police declined to say where they are being held.

The home on Gardner Street was claimed by the city last year because of unpaid taxes, according to the Allegheny County property assessment Web site.