It happened at an enclosed slab next to a mobile home in Turner.
Riley Davis died at Maine Medical Center in Portland.
He was burned on more than 70% of his body after the diesel fuel exploded.
Two other children were also burned in the flashback of flame.
11-year-old Brandon Birney and his 8-year-old sister Bradi, were treated at area hospitals.
Officials tell us that Riley Davis is related to the Birneys, who owned the nearby mobile home, but have not released how.