Four children were killed and four other people were seriously injured in southern Vietnam when a shell believed to be left over from the Vietnam War blew up, police said Monday. The blast Sunday in Vung Liem District, Vinh Long province, killed three children aged between four and 11 instantly and a 6-year-old boy died later in hospital, district police was quoted as saying by DPA. It seriously injured two children and two adult male bystanders, police said. The children had been playing with the shell after they found it under some bamboo bushes.