The incident happened around midnight Tuesday at a residence on the 9300 block of Elm Vista Drive.
Authorities said the victims were all sleeping when the suspects broke in by kicking in the front door. An altercation took place inside and continued outside on the front yard, where the victim was shot once in the head.
"I had just gone to the movies," said neighbor Yovan Nunez. "I came home and I heard two gun shots. I was lying down and I figured someone had got shot."
Police said six adults live in the home with their children, and that they are all family members. They said that the kids were not home during the apparent home-invasion robbery.
"All I heard was screaming, I didn't hear no gunshots," said neighbor Deeann Mendez. "We heard screaming and we came out."
The victim, described as a younger man, was transported to a local hospital in grave condition. Authorities don't believe the victims were targeted.
Neighbors said the family moved in just before Christmas.
Mendez says that because of incidents like this, she doesn't let her kids play outside.
"We moved in and found out later that this is one of the worst streets in Downey," said Mendez. "So yeah, this is the last straw. I think we are going to be moving from this street."
Investigators said the suspects fled the scene in a small, light-colored compact vehicle driving toward Bellflower Boulevard.
Anyone with information related to the case should contact Downey Police at (562) 861-0771.