Nguyen Thi Kim Ngan, 10, Nguyen Huu Bao, Ngan's 7-year-old brother, and Pham Dinh Chien, 8, slipped into the pond, about two meters deep, while playing in a coffee garden in Dai Lao Commune of Bao Loc Town with several other children.
The other children then ran off to call for help from adults. The three were retrieved from the pond, but could not be revived.
The pond was intended for watering coffee plants, said Pham Cong Huong, deputy chairman of Dai Lao Commune people's committee. Authorities are still trying to verify whether any other children also fell into the pond, so the pond is being drained, he added.
Child drowning is not uncommon in Vietnam, with the WHO estimating 11,000 such deaths a year.