Maria Mendoza says she saw the flames all over the boy shortly before Smithfield fire fighters and the rescue squad showed up to her home in the 200 block of Sunrise Ave.
Her husband says he recalled his wife heard the loud bang outside their home.
"She stayed about five minutes inside the house then after five minutes she listened -- big noise like [an] explosion," Victor Billagomez said.
Billagomez says several neighbors, including a retired state trooper, stepped in to help by calling 911 and calming down the boy.
The 9-year-old was rushed to Johnston Medical Center and then flown to the NC Jaycee Burn Center at UNC with third-degree burns all over his torso and hands.
Before that, Billagomez says his wife tried to pull off the boy's cloths and spray water in the yard.
"When she tried to clean it up everything, she found a little lighter inside his pants," Billagomez said.
The child, who lives up the street from the couple, had originally come to their home to play with their son.
They believe he wandered off in their backyard and sparked the fire near their shed.
"I got my lawnmower right there and I keep gasoline, just a little bit, not too much," Billagomez said.
No one else was hurt in the incident.