A Chevy Silverado traveling behind the Tahoe ran over the 1-year-old, police said.
The baby, who was not in a car seat, was taken to an area hospital with life-threatening injuries. Police said the mother claims the child was wearing a seat belt.
The child was among four children in the SUV without car seats.
"At this time, we don't know how he got out," Washington said. "But it's been said that he's been known to open the back door."