Officers were called to an address in Pentwyn, Penyrhoel, Caerphilly at around 3.55pm on Monday 8 November, following reports of a dog attack.
Officers attended, including specially-trained firearms officers, alongside paramedics from the Welsh Ambulance Service, who confirmed that a 10-year-old boy had died at the scene.
The dog was destroyed by firearms officers and no other animals were involved in the attack.
Chief Superintendent Mark Hobrough said:
“Officers will be making further enquiries at this time and will remain at the scene as the investigation progresses.
“It is possible that you may see ongoing police activity in Caerphilly as part of this work. You may have also seen an increased presence earlier today while officers were attending the incident, but please do not be alarmed.
“If you have concerns or information then please do stop and talk with us.”
Anyone with information is asked to call us on 101, quoting log reference 2100392510.