According to officials, the gun was in an antique car that was on display inside the stadium.
The child got his hands on the gun and accidentally shot his mother, who was rushed to Regional One in critical condition, authorities said.
Police said that woman – who has not been identified – has been upgraded to stable condition.
>> Read more trending news
The gun owner has been detained. Police told WHBQ that it is too early to know if they will press charges.
The child involved was an 8-year-old student at Millington Elementary School, according to fire officials.
Officials said the baseball game was canceled, as teams were forced to leave the field following the incident.
The investigation is ongoing.