Jamie Lee Rosales, the boy's mother and Rosales' sister, was also arrested on a charge of injury to a child for failing to protect the boy. She was being held on $50,000 bond.
The 20-year-old mother had signed a safety plan in April with Child Protective Services that advised her not to leave her children with her sister because of the woman's disability, according to charging documents.
A woman who answered the phone at Mayra Rosales' home and wouldn't give her name said the family would have no comment on the charges. Jamie Rosales remained in jail and authorities had no attorney contact information for her.
On the morning of March 18, Jamie Lee Rosales left Eliseo and her two younger children in the sole supervision of Mayra Rosales, authorities say.
Less than two hours later, Mayra Rosales phoned her sister to say that Eliseo had gotten stuck under her bed and his head was swollen, according to the charging documents Eliseo was removed from life support and declared dead that afternoon.
Mayra Rosales would later tell investigators, alternately, that she slipped, landing with her right hand on Eliseo's head while trying to pick him off the floor and that he fell off a chair, according to documents.
But an autopsy revealed that Eliseo's injuries were "consistent with blunt force trauma" and that Mayra Rosales' explanations were inconsistent with the injuries.
The autopsy found multiple skull fractures on the forehead and upper and lower rear parts of Eliseo's skull. The autopsy also found fractures that were estimated to be about a month old, Trevino said.