A three-year-old girl may have tried to change her baby brother's nappy moments before he died in his cot.
An inquest heard that the toddler was alone upstairs with six-month-old Feonyx Clarke, before the baby was found lying limp and face down with four or five nappy bags near his head.
It is believed he may have suffocated on the bags, which were not in the cot when mum Kirsty checked on him minutes before.
Coroner Darren Salter asked Mrs Clarke: "It is possible that she may have tried to change Feonyx? That would be an explanation, wouldn't it?"
Mrs Clarke, 27, replied: "Yes."
However, Dr Steve Gould said Feonyx's collapse in Witney, Oxfordshire, may have had nothing to do with the nappy bags. Mr Salter recorded an open verdict at the inquest in Oxford.
He said: "I think the most likely aspect of this was that it was a natural cause, but it is hard to determine what that natural cause was,' he said. It was a very sad and tragic death."