Officers were called out to a property in Carr Lane, Milnrow, at 1.15pm on Sunday. The boy was taken to hospital by ambulance, where he was pronounced dead.
Greater Manchester Police (GMP) Detective Superintendent Jamie Daniels said the force was probing "previous incidents involving dogs" at the property.
Det Supt Daniels, of GMP's public protection and serious crime division, said: "This is a tragic, devastating incident and our thoughts are with the family at this horrendous time.
"We are investigating the incident and previous incidents involving dogs at this address.
"While our enquiries to find out what happened will be thorough and are very much in their infancy, we suspect that this little boy has, sadly succumbed, to injuries received as a result of a dog attack.
"I understand this is an extremely distressing incident for all concerned and this news will rock the local community.
"I can only assure everyone that we will work relentlessly to establish the full circumstances that led to this tragedy and while we retain an open mind, this is now being dealt with as a criminal investigation."
Police said no arrests have been made, and enquiries are continuing to establish the circumstances leading up to the boy's death, with GMP keeping "an open mind".
There would be a "significant police presence" in the area while GMP investigates, Det Supt Daniels said.
farming background, dogs were *not* allowed in the house, and carefully attended to on the land
waaay too risky - this is simply sad, and a stupid thing Humans do