MELROSE — A 5-year-old boy was shot in the shoulder with his father's gun inside his Westchester Avenue apartment Friday morning, sources said.

The boy's father, who flagged down cops en route to the hospital, initially blamed the injury on a gunpoint robbery at a check cashing site, then later changed his story to say that he was to blame for the shooting, calling it an accident, sources said.

But sources said they believe he was trying to cover up for his 11-year-old son, who they believe may have been playing with the gun when it went off.

Investigators were searching the house Friday looking for the weapon. It was not immediately clear whether it was licensed.

The drama began shortly before 10:40 a.m. Friday, when the boy was injured and the father scooped him up and put him into his SUV to rush him to the hospital, sources said. He spotted a marked police car at the corner of Third and Brook avenues, and flagged it down, asking for assistance.

"The cops we're putting him in the back of the ambulance," said Mickey Garcia, who works at a furniture store on the corner. "He looked shocked."

The boy was taken to Lincoln Medical and Mental Health Center in serious but stable condition, a fire spokesman said.

Neighbors said the man — who they said went by the nickname "Heavy D" and "Papa Smurf," in honor of his beard — was a good father to his two sons. They said he often took the younger one to a park nearby and watched over him while he played.

"He's real good with his son," said Shanee McCray, 30, a neighbor. "He spoils his son."