A 7-year-old Brockton boy was in serious condition Sunday night after he was shot while riding his bicycle in Dorchester hours earlier.The child, identified by relatives as Divan Silva, was visiting relatives and headed to a market for something to drink when he was shot in the rear near 296 Bowdoin St. about 4:15 p.m., police and his family said. The youngster was taken to Boston Children’s Hospital, where a spokeswoman Sunday night said he was in serious condition.Police Superintendent in Chief William G. Gross said at the scene that a bullet also grazed the head of a 20-year-old man. He was taken to Boston Medical Center.Gross said witnesses described the shooter as a light-skinned man between the ages of approximately 17 and 20 whowore a red hoodie and tan pants, and who fled on foot. Gross urged the public to reject the “no snitching” code of conduct and contact police with any information on the shooter’s whereabouts.“Our 7-year-olds should be able to ride down the street,” Gross said. “Heshot a 7-year-old kid. [The public] should turn him in.”Police are investigating a possible motive for the shooting, and officers do not know if the assailant knew either victim, Gross said.“I don’t think the 7-year-old was the intended target,” he said.The boy’s uncle, Enriquo Frederico, 25, said outside his Bowdoin Street apartment that the family does not know the 20-year-old victim. He said he felt terrible knowing that his nephew had been hit with gunfire.“He’s just a kid,” Frederico said. “It’s just bad for 7 years old to say, ‘Yeah, I got shot.’ ”Frederico described his nephew as a good-natured child.“He’s happy,” he said. “Likes to run around, jump.”He said he hopes the shooter is apprehended, and that the family is anxious about what will happen to Divan Silva as he tries to recover.Manny Suazo, 22, a barber at Rodriguez Barber Shop on Bowdoin Street, said he saw Silva lying on the ground by his bicycle in front of the businessafter the shooting.“He was crying,” said Suazo. “That’s not good.”Mayor Martin J. Walsh also condemned the shooting.“These acts of violence have no place on the streets of our neighborhoods,” Walsh said in a statement. “While this incident is still under investigation, my thoughts are with this young boy, his family, and the entire community.”City Councilor Tito Jackson said he was saddened to learn that a young boy had been ensnared in street violence.“It’s extremely heartbreaking to know that individuals would shoot in the vicinity of a 7-year-old child,” Jackson said. “A child at the age of 7 should be making a decision between a big-wheel and a bike, not running from bullets.”Jackson added, “This is unacceptable in any neighborhood in the city of Boston and should cause all of us in every single neighborhood . . . to jump to action, and to want to make sure that the proper resources are out on the streets to protect young people, and to make sure [the perpetrators] are brought to justice.”Separately on Sunday, a man in his 20s was shot in the back near Radcliffe Street in Dorchester, about 10 minutes after Silva was shot, Gross said.That man was in stable condition at Boston Medical Center. Gross said the victim is not cooperating with investigators. He also said there is no indication that the two shootings are related.Anyone with information on either case can call the Police Department’s anonymoustipline 800-494-TIPS or text the word ‘TIP’ to CRIME [27463].Despite the weekend violence, Gross said, police are making progress in their efforts to combat violence. He said Boston police have taken 234 guns off the streets this year, after removing just over 1,000 firearms in 2014.