Marivel Romero tells ABC7 News she was at home when they got a call from someone who said the boy, who was at the event with his mother and other grandmother, was shot.
Romero went from hospital to hospital looking for him. But when she finally got to the right one, she says he was already dead.
She remembers him as "always kind, happy and, you know, playful."
According to Romero, her daughter-in-law and the boy's other grandmother were both shot and have been hospitalized.
When asked about the incident, Romero said, "It has to be someone really sick. Because shooting a kid... it's a family event. I just hope there is justice and they catch the last person or the other person and that there's justice. I want justice for my grandson."
A city official says three victims and one suspect died and more than a dozen people were hurt during the shooting at the annual event.
The California food festival is a nationally known three-day event that attracts thousands of garlic lovers. Sunday was the final day.
Get the latest on the deadly Gilroy Garlic Festival shooting here.