The mother of a 16-year-old boy says her son was beaten in the head Sunday by a Baton Rouge police officer at the city’s celebration of Earth Day as additional officers held the teenager, who was later arrested, face-down on the ground.Baton Rouge police say at least three other boys were arrested in connection to a shooting after a fight at the Earth Day gathering.A video first published by The Rouge Collection appears to show a person being held face-down on grass and beaten in the head by an officer several times as other lawmen rush to hold down or surround the person.Baton Rouge Police Department spokesman Sgt. Don Coppola acknowledged the incident that appeared to be depicted in the video and said Chief Carl Dabadie Jr. has begun an internal investigation into the case.