Witnesses said the boy went into a men's bathroom at Rio Hondo Park about 2:30 p.m. while his mother waited in the car. The boy was then allegedly pulled into a stall by the suspect and was raped.
A witness said the man calmly walked the boy out of the bathroom to the car where his mother waited and said the boy was crying for her.
"The little boy was screaming and he said, 'Here's your mother.' He goes, 'Your son is crying for you,' and the little boy was looking at him frightened saying, 'No, no,'" witness Gia Singerman said. "The mother said what happened, what's going on? And the man lightly just walked away really calmly and the little boy had told his mother that he was raped."
Anthony Contreras lives across the street from Rio Hondo Park. The father of five says the crime has left him rattled.
"You never know who you're dealing with in public," Contreras said. "You're thinking your kid's fine and then to hear what happened and how brazen the guy was to do what he did."
The suspect is described as a white man in his 30s, about 6 feet tall, 200 pounds, with blonde hair, blue eyes and a goatee.
He was seen driving away in a white minivan with a California license plate that starts with "6J."
"We've been working this case constantly, nobody's taking a break despite the weekend and holiday," said Sgt. Michael Thomas with the Los Angeles County Sheriff's Department.
Anyone with information is urged to call the sheriff's special victims unit at (877) 710-5273.