Gardaí say the father and son found near the Royal Canal in Dublin yesterday died as a result of drowning.
The official post mortem results were released late last night.
This incident, which happened at the back of a housing estate near the Navan Road, is being treated as a tragic accident.
Sean Sweeney, who was in his 30s, and his three-year-old son Tyler were using a shortcut to visit relatives in the Ashington housing estate.
Their bodies were found in a ditch with a stream running through it on Sunday last.
Gardaí are investigating whether the two may have accidentally fallen into the water the night before.
Members of the public and relatives have left flowers, Easter eggs and soft toys at a spot close to where the tragedy happened.
Locals say another child died in a similar tragic accident at the same place a number of years ago.
Politicians from the area are demanding improved safety measures.