"Knife wounds of the boy aren't fatal. However his eyeballs were out of the sockets when he was found," the boy's family said.
It was uncertain whether his vision can be restored or not, state-run People's Daily reported.
The incident happened in Yushu village in the province when the victim surnamed Zhu, 12, was taking care of the family's store as his parents worked in the field.
A woman entered the store and bought a bottle of beer. Later she said to the boy that she wanted an ice-cream.
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Later she killed herself by drinking pesticide.
The child told his family that after his eyes were injured, he could not see.
However he felt the woman lit the gas tank inside the house. He came out of the out of the house. The boy's parents who were working in the field saw the smoke arising from their house and rushed home immediately.
They saw the woman lying on the ground, with no breath.
The woman surnamed Wang is a villager who had conflicts with the boy's family, the report said.