Environment Secretary Elizabeth Truss has promised to help Kye Gbangbola and Nicole Lawler find out how their seven-year-old son Zane died after water from a landfill site at a former gravel pit behind their home in Chertsey, Surrey, filled its basement during the flooding last February.
The minister has ordered urgent testing of a lake in the middle of the site for chemical toxins which could interact with water to produce hydrogen cyanide, a deadly gas found in the home after the incident.
However, the parents are campaigning for all landfill sites in flood risk areas to be tested for toxins to stop other families from suffering their anguish.
Landfill sites were unregulated after the Second World War, with no records kept of the large amounts of munitions and gas canisters buried in them.
It took a public outcry at drums of cyanide being dumped at an abandoned brick kiln in Nuneaton in 1971 to shine the spotlight on the problem of chemical waste being illegally buried at sites.
In response the Deposit of Poisonous Waste Act 1972 was drafted in 10 days and passed through Parliament within a month.
With flooding predicted to become a more regular occurrence due to wetter weather caused by climate change, Kye said: "There needs to be an urgent inquiry, not just into why Zane died but into the historical landfill sites in the UK and the consequences of them being flooded."
Zane was taken to hospital along with Nicole, 37, and Kye, 48, after being overcome by fumes during last year's floods.
The schoolboy died and his father was left a paraplegic.
An initial post-mortem examination on Zane's body found "no clear cause of death".
Traces of hydrogen cyanide, used in Nazi death camps in the Second World War, were found in the blood of all three members of the family.
Public health officials and the fire service also found evidence of hydrogen cyanide at the home and evacuated 15 neighbours, yet the family have spent nearly a year battling to be given a cause of death for Zane.
They have not been able to step foot back in their home, even to collect some of their only son's treasured belongings, and have been living out of hotels for the past 11 months.
After recently meeting the parents, Truss ordered immediate testing of the lake for chemical toxins which could react with water to release hydrogen cyanide gas.
In a letter she said: "As a parent I am extremely saddened to hear in our recent meeting more details about this tragic case.
"It is clear on the face of it a number of institutions have some important questions to answer and I was concerned to learn about the slow progress that has been made by a number of bodies in getting to the bottom of what happened."
Kye welcomed the minister's intervention, but wants the land surrounding the lake to also be tested for toxins, as he believes the contamination was caused by floodwater running through the landfill.
He said: "Liz Truss's letter was certainly a step in the right direction, but when we met with ministers we were clear, independent testing of the land needs to be carried out.
"The Government needs to ensure something like this never happens again.
"We have lost a son, yet thousands of other people could unknowingly be at risk. We would like Zane back, it's as simple as that, but we know that can't be done, which is why the campaign aims to make sure lessons are learnt and this does not happen to any other families."
An Environment Agency spokesman said: "This is a tragedy and our sincere sympathies are with the Gbangbola family. Along with other agencies we have worked with Surrey Police on its investigation and we now await the coroner's findings."
A spokesman for Surrey Police said the details of its lengthy investigation have been passed to the coroner, adding: "It would be inappropriate to comment further at this time."
Click here to watch the video of the parents speaking