Gatineau parents have launched a petition to find out what was in the McDonald's chocolate milkshake that allegedly caused their son's mouth to burn last summer.

Jon Hansen told CBC News that his family rejected settlement offers worth thousands of dollars from McDonald's Canada in favour of a lab report on the contents of the milkshake. He's concerned there might have been something in the milkshake that could cause long-term complications for his six-year-old son.

"Who cares about the money. We want the report. At the end of the day, that's what its all about," he said.

"Even if we get money and everything, what happens if this happens again in the future and we knew about this? How can we live with ourselves?"

McDonald's milkshake Gatineau parents

Jon Hansen and Jennifer Cameron want to know what was in a McDonald's milkshake that allegedly burned their son's mouth. (CBC)

Pierce Hansen, then 5, described a burning sensation in his mouth after drinking a milkshake from a Buckingham McDonald's on July 22, 2013.

"My tummy was hurted," he said.

His mother Jennifer Cameron said she tried the drink, as well.

"It was like having wasabi. It was so strong going through my face," Cameron said. "My mouth was burning and I knew there was something wrong with it."

McDonald's spokesperson Jason Patuano said the company conducted an investigation through an independent third-party lab. The results were inconclusive, but Hansen said McDonald's admitted to the family's lawyer that "a small amount of store-related compound" was found in the milkshake.

McDonald's issues statement

On June 11, McDonald's Canada issued the following statement:

"At McDonald's Canada, food quality and safety is our top priority and we have strict food safety policies and procedures in place to ensure our customers receive the highest quality products when they visit our restaurants.  

From the outset, McDonald’s has been in regular contact with the family since the alleged incident. We appreciate the parents’ desire to know what their child may have ingested and regret it has taken so long to address this situation.  

Upon learning of this situation, we immediately began a thorough investigation and as is our usual process, engaged an independent third-party laboratory to test the contents of the milkshake which were purchased through a drive-thru.  Unfortunately, the lab was unable to determine the source however was able to confirm that there were no cleaning solutions contained in the child’s milkshake as was originally alleged. We also confirmed that a total of 63 milkshakes were sold in the restaurant that day without any other complaints being reported. 

These results were shared with the family last August and we have tried unsuccessfully since then to work with the family to reach an equitable resolution."