The child was taken to Airedale General Hospital by ambulance where he was pronounced dead.
A murder investigation was launched by West Yorkshire Police's Homicide and Major Enquiry Team and at 11:30am this morning and a 32-year old man was arrested from an address in the Ingrow area of Keighley.
More top news
Detectives leading a criminal investigation into the disaster want to speak to 19 people seen on CCTV at the stadium that day.
The brothers were greeted by fans after winning gold and silver in the triathlon at Rio 2016
The medal-winning duo, who live and train in Leeds, say they've been amazed by the reception on returning from Rio