At around 2 p.m. the children were playing near the canal on TX33 Street in Thanh Xuan District.
But when their mother came to check on them, she could not see them anywhere.
After she and her neighbors searched for almost two hours, they found the body of the boy in the canal. An hour later they found the body of the girl.
The canal was created more than a year ago from a branch of the Vam Thuat River, a tributary of the Saigon River. It is surrounded by 70-cm barriers but, where the tragic accident happened, a three-meter section is missing.
"If the barrier had not been missing, the kids could not have fallen into the canal," a local named Nguyen Duc Thang said.
The police are investigating.
In the first five months of this year 113 children died due to drowning across Vietnam, according to the Ministry of Labor, Invalids and Social Affairs.
A 2020 report by its Department of Child Affairs said drowning is one of the major causes of death of children aged 12-15.
Every year the country records 2,000 drowning deaths on average, the highest in Southeast Asia.