The incident occurred when the victims were marching in second line parade, a common event in New Orleans. Local police said the attack occurred around 1.45 pm at an intersection.
Initial reports said 12 people were injured but the number later rose to 19, police said. The reason behind the shooting was yet to be ascertained.
The injured included a 10-year-old boy ands a girl and seven women. Both the boy and the girl had graze wounds and were doing fine, while two adults reportedly underwent surgery later in the day.
Authorities said panic struck the area as people started running immediately after the shooting. One of the suspects was a man aged between 18-22. Investigators were collective evidence to get leads into the case.
New Orleans Mayor Mitch Landrieu has appealed to the people who have information to come forward.
Sunday's incident revived the dreadful memories of April 15 when terror attacks in the historic Boston marathon killed three people including a eight-year-old besides injuring over 260.