The children, a boy and his younger sisters, were found by a villager while struggling with convulsions after taking the poison late Tuesday at their home in Bijie in the remote province of Guizhou, the official Xinhua news agency said, highlighting the plight faced by rural children left behind by their migrant guardians.
They soon died and police believe it was a suicide.
Their mother left in March 2014 after being beaten up by their father and her whereabouts are unknown.
The father, identified as Zhang Fangqi, left the town to work elsewhere in March, wiring money back periodically, Xinhua added, citing the Communist Party chief of the village and a family relative.
The children had apparently suffered severe domestic violence in previous years and the boy had attempted to commit suicide before.
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At one point the child's left arm was broken and his right ear was torn by his father, the relative said.
In August 2012, he ran away from home for more than 10 days and was later made by his mother to stand under the sun naked for over two hours as punishment, the relative added.
Offspring of China's vast army of migrant workers, referred to as "left behind children", often stay in their rural homes, usually with their ageing grandparents, partly because access to kindergartens and schools in cities is either extremely hard to obtain or expensive.
Incidents involving such children often make headlines in China, including one in Bijie in November 2012, when five boys aged about 10 were found dead in a dumpster after they climbed inside to escape the night-time cold.
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