In the early evening of Sunday, officers were sent to an address in Rogiet, south-east Wales.
A nine-month-old baby was pronounced dead at the scene. It is not clear whether it is a boy or a girl.
Police report that the dog has been seized and removed from the property. How the tragedy could happen is still unclear. The police are still investigating.
Local residents are in disbelief about what happened. Local authorities are providing assistance to local residents.