A 9-year-old Brooklyn boy was shot twice last night trying to retrieve a bicycle that he believed had been stolen from a relative, authorities said.

Ronnell Gurley was struck in the arm and back near the Breukelen Houses in Canarsie at 9 p.m.

Authorities said that about an hour earlier, a bicycle had been swiped — and Ronnell and some pals had been looking for it. They spotted a teenager with the bike in a grassy area outside the housing project.

But when the group of children approached the teen, he pulled a gun and opened fire, police said.

“I can’t believe these kids and guns today,” said the child’s grandmother, Edna Gurley.

“When I was young, you would end it with fists and shake hands. A stray bullet doesn’t know it’s going to hit a 9-year-old.”

Ronnell was taken to Brookdale Hospital with a fractured arm and a back wound.

Police sources said last night they had five youths in custody, ranging in age from 12 to 16.