A prison work crew baby-sat a 2 1/2-year-old boy who was spotted Friday running along the center lines of a rural highway in Maryland as trucks loaded with gravel rumbling by, police and correctional officials said. The six minimum-security inmates shared their lunches with the toddler, who apparently wandered away from home, and played with him while authorities located the parents and investigated, said Correctional Officer Gary Kershner, who was overseeing the prisoners. “Me and my inmate crew, we just kind of baby-sat for the next three hours,” Kershner said. “They were as much entertained by the child as he was by them.” The boy was on Route 550 not far from the Pennsylvania line, when a dump truck driver stopped to pluck him off the road shortly after 9 A.M., said Trooper First Class David Greenwood, who was at the scene. Kershner, who had stopped his van to help, said the truck driver handed the boy to him for safekeeping until police arrived. A State Highway Administration truck driver accompanying the litter-picking crew also stayed on the scene, agency spokesman Charles Gischlar said.