Jonathan James died from dehydration in Dallas after his father and step mother allegedly denied him water as punishment after he took some guitar strings from one of his siblings.
Michael Ray James and Tina Maria Alberson have been arrested and charged with injury to a child.
The boy’s grandmother said that his twin brother had wanted to help, but was afraid he would be punished too.
‘I did tell him, “I don’t want you to feel guilty because there’s nothing you could do.” And he says, “I wish I had snuck him some water”,’ Sue Shotwell told Fox Dallas-Fort Worth.
She said she is now concerned for the twin, who is called Joseph, because he watched his brother collapse and has been having nightmares reliving the moment he died.
The boys had been spending the summer with their biological father because of a custody arrangement.
Mrs Shotwell said they had been reluctant to go.