Police did not believe the child is in danger while he was missing. They said his parents are in a bitter custody dispute.
The father, Rommel Rodriguez, possibly drove off in a white, four-door sedan. He has two cars registered to him - a 2004 VW Jetta, with Arizona license ABW9656, and a 2004 VW Toureg, with Arizona license AMXDF2. His last known address is in Phoenix, Arizona.
Sinclair is described as a male Hispanic, 3 feet, 6 inches tall, about 43 pounds, with black hair and brown eyes. He was last seen wearing a brown shirt with a monkey picture and the words "No Dating Allowed" on the front, with plaid shorts and green and black shoes that light up.
Anyone who has further information related to the case was urged to call the Fullerton Police Department at (714) 738-6715.