Travis Stratton was at home in the care of his grandparents when he wandered out of the house. He was reported missing at about 1:30 p.m. on the 32500 block of The Old Road.
He was found a couple of hours later in a neighbor's backyard pool up the block.
"Deputies immediately jumped in the water, pulled him from the pool," said Dep. Joshua Dubin with the Los Angeles County Sheriff's Department.
The deputies carried the boy to a patrol car and rushed him to a waiting helicopter. They airlifted him to Henry Mayo Newhall Memorial Hospital in Valencia but were unable to revive him.
Authorities are still investigating how the boy got into the neighbor's swimming pool. The property reportedly has walls around it and a locked gate, as well as dogs that usually bark when people walk by, according to neighbors.
Neighbors say Travis had autism. They described him as a sweet and playful boy.
"It's just hard because they are such a great family. All they do is take care of him. It's just so close to home and you find out that one of your family's kids is missing and you find out he's in the pool," family friend Heather Martinez said through tears.
The sheriff's department says this appears to have been a tragic accident.
"It's an extremely difficult situation, not only for the family, obviously losing a child, but for everybody involved in the extensive search," said Dubin.