The incident happened just after 8 p.m. at the Budget Inn on Old Interstate Road.
Police said that when they arrived at the scene, they found Robinson and his 3-year-old brother, who had been grazed by a bullet inside one of the hotel rooms.
The 19-year-old had been grazed in the shoulder and the toddler was grazed in the head, according to police.
>> On WSOCTV.com: 1-year-old girl, woman hurt in 'accidental shooting' at party, police say
Police said they determined that the 3-year-old victim found the unsecured gun and accidentally fired.
Officials said the injuries are not life-threatening.
Police at the scene said the brothers' mother also was in the room at the time of the incident.