Aidan Sands died in June 2011 after being found at the bottom of the pool at the Red Lion Caravan Park in Arbroath. He had been taken to Ninewells Hospital in Dundee but never woke up, and died four days later.
Three years on the Crown Office has still not yet decided whether charges under health and safety legislation will be brought against the campsite's owners, Loch Earn Caravan Parks Ltd, based in Errol, Perthshire.
Aidan's family want to find out why he died and ask questions about staffing at the pool at the time of the incident. They suffered another tragedy when Aidan's 36-year-old mother Mandy died last February.
Her parents, Tom and Kathryn, both 58, have taken over the case and legal papers have been served on the campsite's owners.
Loch Earn Caravan Parks Ltd declined to comment on the case.
A spokesman for the Crown Office and Procurator Fiscal Service (COPFS) said it was still considering the case. He said: "Police Scotland and Angus Council carried out a joint investigation under the direction of COPFS into the death of a six-year-old boy on June 22 2011 after an incident on June 18 2011 at the Red Lion Caravan Park.
"A prosecution report has now been submitted to the COPFS and remains under consideration by our health and safety division."