A six-year-old boy was buried today in St. Louis after he was killed last week in an gun attack his parents say stemmed from a traffic dispute . Marcus Johnson Jr visited O'Fallon Park with his parents , four siblings , and other friends and family members while recovering from heart surgery one week earlier . He had a post-operation appointment the day he was killed . Police are searching for the occupants of a car who shot at the family 's minivan as they left the north St Louis park in a minivan at about 7.30pm on March 11 . Marcus Johnson Jr. 's parents figured a day at a city park was just what the 6-year-old kindergartner needed while recovering from heart surgery the previous week . Instead , his family buried Marcus today after the child was shot in the chest and killed in an attack his mother and father said stemmed from a traffic dispute . Marcus Johnson Sr. said he returned fire in self-defense as the rolling shootout continued for several blocks . Marcus 's 15-year-old brother and a 69-year-old family friend were also wounded . 'My baby already had stress to live in this world , and for somebody to take his life away is wrong , ' mother Quiana Johnson told the St Louis Post Dispatch . She said that Marcus , who was in kindergarten , had suffered from a heart ailment since birth . His family had to watch him closely because he was taking blood-thinning drugs so he had to be careful not to get bruised . 'He was a happy , happy , loving and caring kid , ' she told the St Louis Post Dispatch . 'Through his sickness he was happy . ' The day of the shooting , the family had piled into their recently purchased 2006 Pontiac Montana and headed to the park . Quiana Johnson said it 'was a nice day ' and that it gave them a chance to 'get out of the house and do some things as a family ' . She said that as they were leaving , her husband saw someone he knew and stopped his vehicle to chat , annoying another man who was stuck because of the traffic . Quiana Johnson said the man told them it was his 'hood ' and that the family should n't hold up traffic . Marcus suffered from a heart ailment and had surgery the week before he was shot . He had been at a post-operation appointment prior to going to the park . His mother said he was taking blood-thinning drugs and had to be careful not to get bruised . The family returned to the car and as they drove to the exit of the park , the man followed them and began shooting . Quiana Johnson had a gun on her - which she had recently bought because of a fear of break-ins in her neighborhood - and when she noticed her son had been shot , she handed it to her husband . ' I told him that if he did n't shoot back , they will kill us all , ' she told the St Louis Post Dispatch . She crawled to the back of the van , where her son had been shot and the rest of her family members were huddling . ' I said , `` little Marcus , wake up . Do n't go to sleep . Mommy is right here with you . Wake up . '' He was trying , ' she said . Once they escaped the shooting they called the police who took Marcus to Barnes-Jewish Hospital , where he was pronounced dead . Funeral arrangements were taken care of at Ronald L Jones Funeral Chapel in St Louis . Johnson said Marcus , his youngest son , was diagnosed with a heart ailment as an infant .
Marcus Johnson Jr was shot as his family was leaving park in their minivan . The gun battle supposedly stemmed from a traffic dispute , mother says . Marcus had heart surgery a week before the incident and a post-operation appointment the day of the shooting . His 15-year-old brother and a 69-year-old family friend were also wounded .