Officers from the New York and Harrisburg police departments, along with members of the United States Marshals Service, converged on the van parked on a Harrisburg street about 10:20 p.m. on Monday, said Pierre Ritter, the chief of the Harrisburg City Police Department. Inside, the officers found the children — seven boys and one girl, ranging in age from 11 months to 11 years — as well as their mother and father, who were arrested.“The kids were in the van,” said Travis Clark, 41, who described a swirl of flashing lights as officers surrounded the van outside his home. “One officer had the baby in his hands.”The developments brought to a close the family’s disappearance and a robust police search. The children’s biological parents — Shanel Nadal, 28, and her boyfriend, Nephra Payne, 34 — were accused of taking them during a supervised group visit on Sept. 19 at the Forestdale child care agency in Forest Hills, Queens. Investigators believe that Ms. Nadal ferried the children out to a black Chevrolet Suburban, where Mr. Payne was waiting, but at some point they switched to the black Ford Econoline van in which they were found, said Paul J. Browne, the chief spokesman for the New York Police Department.After the disappearance, the trail led to South Carolina, where detectives knew Ms. Nadal had relatives. Mr. Payne and Ms. Nadal also lived for many years in South Carolina, though they had most recently been living on Amsterdam Avenue in Manhattan.Detectives from the city’s 112th Precinct determined that the couple stopped at a gasoline station and convenience store in Holly Hill, S.C., on Friday. Videotape recovered from a surveillance camera captured Mr. Payne’s image and Ms. Nadal’s voice as they bought gas for the van, Mr. Browne said. Because the officers could not confirm that the children were with their parents, they continued investigating.The next night, those detectives determined that the couple had driven to Pennsylvania, where Mr. Payne had a brother living in Harrisburg. A second team of city detectives, went there. Chief Ritter said the New York detectives “acquired a cellphone number” that Ms. Nadal had used; investigations determined that she had made several calls from the Harrisburg area.When the police raided the van, on a street near Mr. Payne’s brother’s house, Mr. Payne collapsed “for some undisclosed reasons” and was taken to a nearby hospital, said Robert J. Philbin, a spokesman for the City of Harrisburg.He said that Mr. Payne was in stable condition and that Ms. Nadal was taken to a local jail.The Queens district attorney, Richard A. Brown, said the couple was awaiting extradition and would face second-degree kidnapping charges, among others.“This is a sad story of a mother and father who have jeopardized their children’s safety by allegedly kidnapping them and taking them out of state,” Mr. Brown said in a news release. “These parents have now also put at risk the very relationships they were supposed to be building with their children during their supervised visits.” The children were placed in foster care in 2009 after charges of abuse and neglect were made, two people with knowledge of the case said.