The 12-year-old son of a retired NYPD sergeant happily shook his neighbor’s hand before hopping on his bike to pedal to the bodega where he was fatally shot — the innocent victim of a possible gang beef, the resident and law-enforcement sources said Sunday.

Tragic Jacob Freytas was struck by a stray bullet during the senseless shootout in a gang-infested area of The  Bronx on Saturday, leaving his family and neighbors distraught over the loss of the bubbly boy.

“Especially his mom — she’s devastated,’’ grieving neighbor Walter Calon said Sunday.

“I saw him just before he left,” Calon recalled of Jacob. “I shook his hand and said, ‘Look out for your little brother and sister.’

“ And then less than a half-hour later, I got a call from my mom and I just dropped the phone right out of my hand.

“I ran back and everybody in front of the building was crying,” said Calon, 56. “Everybody on the block was crying.”

Jacob had pedaled to Wanda Deli Grocery at Elliott Place near the Grand Concourse shortly before 5 p.m. when he was fatally struck by a stray bullet as a possible gangbanger opened fire at rivals, sources said.

The Mount Eden neighborhood is known territory for the violent Trinitarios and Sev Side Pinni street gangs, and sources said police are probing if the crews were behind the shooting.

The suspected gunman got into a dispute with another group outside the bodega, with the beef escalating when the shooter pulled a gun and opened fire, sources said.

Heartbreaking security footage shows the youngster stumbling back into the shop clutching his chest before he collapses.

The tragic youngster’s father is retired NYPD Sgt. Jesus Freytes, who worked in The Bronx,  sources said.

The shooting, which also left two combatants wounded, devastated the young victim’s family, with his mom so distraught that neighbors said she was staying at a local hotel because she could not bear the pain of being home.

“She’s not OK,” Jacob’s aunt sobbed. “She can’t come down here. She can’t, I’m sorry.”

Sources said police have a person of interest in custody, but no charges have been filed and police are trying to determine what sparked the bloodshed.

“He was a bright kid,” Calon said of Jacob. “He’s a good kid. He always saluted me.

“He played sports, he’s always playing here in the front court. I’ve known him for 10 of his 12 years. I saw him grow up.

“I don’t understand,” he added. “I’m feeling for the family right now, especially his mom.”