The toddler was playing the yard while his grandfather was mowing the lawn at the boy's home, Sheriff Bill Elfo said. At some point, the grandfather backed over the boy, killing him instantly.
"It's what appears to be a tragic, freak accident," Elfo told the Bellingham Herald.
A memorial service will be held Friday, the Herald reported. Elfo asked that the boy's identity not be released to protect the privacy of the family.