A gunman riding a bicycle reportedly fired a gun in the direction of the boy's house.
The shooting occurred at approximately 4:40 p.m. near Wilson Avenue and Nuevo Road.
The suspect was reportedly riding a red bicycle and fired five rounds.
The 4-year-old boy was grazed by one of the bullets while he has playing outside.
The boy was hospitalized and treated for a non-life-threatening injury, according to the Riverside County Sheriff's Department.
Sheriff's department gang investigators were on scene.
City News Service contributed to this report.