A 6-year-old boy was nearly killed when his neighbor allegedly opened fire as the kid picked up his bike from the sidewalk -- and the man's already sprung from jail after posting a shockingly low bond.

The incident went down over the weekend in Ypsilanti, Michigan -- about 35 miles outside Detroit -- where the boy, Coby, is lucky to be alive after the neighbor allegedly chased him with a sledgehammer, and then fired a gun, hitting him in the arm.

The neighbor, Ryan Le-Nguyen, was reportedly pissed Coby and a friend had left their bikes in front of his home's sidewalk. The boy's father, Arnold Daniel, told FOX2 when the boys returned to get the bikes ... Le-Nguyen went after Coby with the hammer.

Coby told FOX2, "He tried hitting me with a sledgehammer but that's not going to work because I'm too fast. (Then he) got a gun and BOOM shot me right here."

As you can see from the video ... the kids, understandably, panicked and fled when they heard the gunshot. You can hear Coby wailing in agony while another kid's screaming "Coby got shot!!!"

Coby's father said the bullet went through his son's arm, but doctors told him had it been an inch in either direction it likely would have killed Coby.

Le-Nguyen, who's reportedly beefed with the family over bicycles in the past, was arrested and charged with assault with intent to murder. He posted a $10k bond on Tuesday ... prompting Coby's angry father to ask how the bond could be so low after Le-Nguyen allegedly tried to kill his son.

Even prosecutors say they requested a $100k bond, but were shocked the judge gave Le-Nguyen $10k cash bond. Prosecutors have since filed an emergency motion to cancel the bond.

As for Coby ... he's home and thankfully expected to make a full recovery.