Police said the boy was walking with his mother Wednesday when a man came up from behind and put a knife to the boy's waist.
The man demanded the boy's mother's purse, but she told him she didn't have any money.
Investigators said the suspect held the knife to the child three times before getting away with the mother's purse and other belongings.
The suspect is described as Hispanic man, 35 to 37 years old, 5 feet 4 inches tall, weighing 180 to 190 pounds with dark complexion. He was said to be wearing a blue hat and a blue T-shirt.
If you have any information regarding this incident, you're urged to call Santa Ana police at (714) 245-8400.