Four schoolchildren were killed when the CNG cylinder of a van, they were travelling in, exploded in Jogeshwari on Monday. The explosion took place in the Millat Nagar area of suburban Oshiwara, police said. ''The children are from the Millat High School and had boarded the Omni van to go home. As the driver started the van, the CNG kit exploded killing the three girls instantly,'' said police.