The child, believed to be 5 or 6, was found around 5 a.m. near 73rd Street and Avalon Boulevard. Police say he was wearing a black Angry Bird T-shirt with blue jeans and dark colored tennis shoes.
Police say the boy was very shy and didn't tell them much, but it appears he was abandoned on the street.
"Through the Department of Children and Family Services, we learned that he told one of their social workers that his mother got on the bus and said goodbye to him and just took off. I don't know if that's true or not, but it's just something we have to check out," said Detective Michael Falvo with the LAPD.
A Good Samaritan heard the boy crying and went outside to see what was going on. Lynn Boyd said she found the cold, frightened child in her yard.
"He just grabbed hold to me real tight and started crying and then he started throwing up," she said.
She said he was asking for his mommy. Boyd and her husband, David, believe the boy was thrown over a wall.
"He had dirt in his head, so we know he hit the ground back here," said David Boyd.
The boy wouldn't say much to the Boyds or their neighbor.
An LAPD detective said the boy's aunt and uncle came forward after media coverage. The boy's mother may have had a medical emergency.
Detectives aren't releasing details about the mother's condition or how the boy wound up in a stranger's yard. They say they're still investigating.
The boy remains in protective custody as investigators try to sort out why he was abandoned in the first place.
Anyone with information was asked to call the 77th Street Police Station at (213) 485-4175.