"He felt he was Spider-Man. He was running and jumping and doing things you see Spider-Man do," said the boy's grandfather, William Shannon.
Soon after, he said he saw two armed men in their 20s in an alley behind the house about 2 p.m.
Shots rang out and one bullet struck the boy as he was heading into the house to get his coat.
"He never saw it coming," Shannon said. "The bullet struck him in the back of the head and it exited in the front of his head."
His uncle was shot in the leg and a bullet grazed his grandfather's wrist.
The boy was transported to Harbor-UCLA Medical Center and was listed in grave condition as of Monday afternoon.
His heart remained strong but there's been little improvement in his overall condition.
Police said the shooters are apparent gang members and one of them used a semi-automatic handgun. Authorities said the Shannon family has no gang affiliations.
"We believe that our suspects are gang members and mistaken this family as rival gang members, even though they're not," said LAPD Detective Christ Barling. "I'm assuming that these cowards were not trying to shoot a 5-year-old kid, and hopefully someone will come forward and turn these cowards in."
While the Shannon family wants the suspects caught, their main focus is the little boy's recovery.
"As far as being angry, I have to make sure that I channel my energy and my thoughts on my grandson," said the boy's grandfather."I'm so proud of him. I love him so much."
A description of the suspects was not immediately available.
They were seen running eastward down the alley toward Central Avenue.
Anyone with information regarding the shooting is urged to call Crime Stoppers at (800) 222-TIPS or (800) 222-8477.
If you'd like to send well wishes:
The Shannon Family
P.O. Box 180203
Los Angeles, CA 90018
City News Service contributed to this report.