The little boy was found with a gunshot wound in his chest when deputies from the Montgomery County Sheriff's Office arrived around 4:15 p.m.
Authorities said the family was celebrating the boy's birthday and heard a gunshot while everyone was playing cards.
RELATED: 11-year-old shot and killed 4 years after praying for end to gun violence in video
Investigators said the child may have found the gun after it fell out of a family member's pocket.
The boy was rushed to a nearby fire station where he died shortly after, deputies said.