The 2-year-old, who suffered a single gunshot wound to the temple, was in critical condition Saturday night at Ben Taub Hospital. The shooting occurred Saturday afternoon at a home in southwest Houston.
Police Sgt. Cameron Grysen said the boys had been arguing when the 2-year-old threw a toy at his brother. The mother thought the boys had returned to their room, but they had instead gone to her room, where the older boy took a loaded gun from the woman's purse.
"The 4-year-old was angry ... he went and got the gun, put it to his brother's head and shot the gun," Grysen said.
The mother told police she had the .32-caliber automatic to protect her family because of recent neighborhood burglaries, and that Saturday was the one day that she did not secure the weapon. She could face criminal charges.
Authorities said the 4-year-old didn't seem to understand what he had done.
"He's wondering where his brother is, and when his brother's coming back," Grysen said.