Four children were wounded after a detonator exploded as they were installing it into a flashlight on Sunday in the southern province of Dong Nai.
Thirteen-year-old Do Van Phuong and his brothers and cousins found the detonator in his family's farm. They thought that was a battery and put it in a broken flashlight, said Do Van Chuong, Phuong's father.
The detonator is suspected to be a remainder of the Vietnam War.
The children received injuries to their eyes, arms, legs, necks, chests, and stomachs. Phuong suffered the most severe injuries.
"The fingers of Phuong's right hand were broken while his left hand, face, and some other parts were also harmed," said doctor Nguyen Bao Tuong of Ho Chi Minh City's Children Hospital No. 1.
Phuong was transferred to HCMC Eye Hospital for further treatment on Monday.
"Phuong's right eye has been seriously damaged. We need time to follow this case to see whether we can save the eye or not," said Vo Thi Chinh Nga, deputy head of the hospital's pediatric department.
Do Van Duong, Phuong's brother, is being treated at Dong Nai Province's Children's Hospital while two of his cousins have been discharged.