Two village heads were fired and three other officials including the district education chief were suspended from their work and were being investigated, according to a statement by the Qixingguan district government in the southwestern city of Bijie.
The district government promised to take proper disciplinary action after the investigation.
Chinese Premier Li Keqiang also demanded that local governments be more careful in providing aid services. He asked that such tragedies not occur again.
Bijie, in impoverished Guizhou province, was the location of another childhood tragedy about three years ago when five runaway boys became asphyxiated after lighting a fire in a garbage bin where they were sheltering from the cold.
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In the latest incident, the siblings were found dead Wednesday at home in their village of Tiankan after ingesting liquid pesticide.
State broadcaster CCTV said the eldest child left behind a suicidal note in which he wrote, "This matter has been planned for a long time, and today is the day to go."
The father had sent the children money, and police recovered a bank card with a balance of nearly USD 600, state media reported. Yet, the children may have had psychological problems because of the long absence of their parents, fellow villagers told state media.
The children usually kept to themselves, local residents said. They also failed to attend school and did not open the door when village cadres and teachers visited them in attempts to bring them back to school, state media said.