"Unfortunately the 14-month-old was a little bit beyond us at that stage," the spokesman said.
Barbara Dunn, spokeswoman for Nelson police, said officers were called to the address after a report of a sudden death.
"The matter has been investigated and has been referred to the coroner," she said.
His parents, Rebecca Malthus and Adam Hicks, have asked for privacy as they deal with the tragedy.
Messages of support have appeared on Ms Malthus' Facebook page. A cousin, Nicole Begg, confirmed the sad news to shocked friends.
"There has been a devastating family tragedy and it is a very sad time for Adam and Rebekah. Please respect their request for absolute privacy and Rebekah has asked for no phone calls from anyone for the next while."
Another, Prue Fothergill, said: "Thinking of your family today as you begin the tragic journey of firsts without your precious baby Mac."