Marshall McClain was the beloved son of Jim and Denise McClain. He was born in 1965 and died in 1978 from unknown causes. His grave was dug and buried by Old Man Corcoran. Whether he was a good kid or a bad kid is unknown. After he passed away he meet with the ghosts of more children who also died and were buried in the same graveyard. Also It's possible he may have lured these children one by one.
The other kids were Ron Jacobson, Scott Wolden, Laura Ayers, Mary Alice Reardon and Cissy Vernon. They were also dug and buried by Old Man Corcoran. Marshall McClain was either evil or vengeful and was trying to take the lives of other children down with him and to join them for their hide and seek group.
In 1993, Marshall and his friends met two new kids named Jack & Kenny Harris who just moved to the neighborhood. it's possible that Marshall and his friends were only visible to other kids, or those they were trying to take down with them. Marshall invited them to join their group for a game of hide and seek in the graveyard.
Marshall's friend Cissy not wanting anyone else to join tried to scare them away by telling them about the ghost who haunts the graveyard named Old Man Corcoran. He just dismissed this as a lie and told them not to listen. Also he and his friends didn't believe them when they said they ran home scared after seeing Old Man Corcoran.
Marshall gave Jack and Kenny another chance to join their group by being it together, while he and his other five friends would hide. Near the end of the game, he popped out from an open grave. Then he tried to convince Jack and Kenny to climb and hide in it with him saying it is the perfect hiding place they can NEVER find you in here! He was just trying to bury them alive and send them to an early grave.
Marshall vanished when Old Man Corcoran appeared. Old Man Corcoran saved Jack and Kenny just in time and revealed the truth about Marshall and his friends to them.