It is thought the child came out of his home suddenly and was hit by the digger. He died on the spot.
Police have launched an investigation into the death. The child's father said the death was the family's mistake for letting the child wander out.
In another development, two trucks and two cars were involved in a pile-up on Sail Road — the road that links Taif to Makkah — on Sunday. No one was killed in the crash. The drivers of the two cars sustained major injuries, while two passengers in the car suffered minor injuries.
Traffic and Civil Defense officers attended the accident and freed one of the drivers who was trapped in the wreckage. All of the injured were taken to King Abdul Aziz Hospital in Taif.