The San Antonio Express-News said the child hopped a chain link fence and went into his neighbor's yard. The dog was chained but the child was within the dog's reach, said police in Montgomery County, about 40 miles north of Houston. The boy's older sister pulled him away but the animal had already done severe damage.
Paramedics rushed the child to a nearby hospital but the boy died.
"It's a real tragedy," neighbor John Roach said. "They're good kids from a good family."
Police said charges are unlikely because the animal was properly restrained. Montgomery County Animal Control has taken custody of the dog.