Mum of murdered toddler Mason Parker opens up about marrying the killer after son's death.

The mother of murdered Queensland toddler Mason Parker – who was killed by her partner – has spoken publicly for the first time.

Speaking to 60 Minutes, Cindy Sandeman said she “never contemplated” the possibility that her partner Troy Reed could have been responsible for son’s murder.

Mason Parker was just 16 months old when he was killed in 2011. He suffered a fractured skull and had 50 bruises all over his tiny body.

Mason's official cause of death was abdominal injuries, which led to a ruptured bowel.

Just eight days before his death, in April 2011, childcare workers noticed severe bruising on the back of Mason's legs, back and bottom. They did not notify authorities.

Just over a week later, Reed put in a panicked call to emergency services, claiming the 16-month-old was "turning blue" and "not responding".

When the paramedics arrived, Mason was already dead. Reed told emergency services that Mason had suffered the horrific injuries after falling from his bed.

But despite police knowing instantly that the injuries were a sign of something much more sinister, Sandeman said she "never contemplated" her partner could be to blame.

"He came across as a nice, caring man. There was nothing crazy going on. No drugs, no alcohol," she told 60 Minutes reporter Allison Langdon in her first public interview since her son's death.

"You never...you don't sit there and think this man that says he loves me and is here and doing all these things and has kids of his own...you just don't think it and that's where I was at," she said.

"It was something that I didn’t contemplate. Because no one that I know is capable of doing that."

"That was clearly a child that was being abused" | Police knew it could only have been one of two people who killed Mason - Cindy or Troy. pic.twitter.com/LDugi0fp81

— 60 Minutes Australia (@60Mins) February 26, 2017

Despite police suspicions, Sandeman stayed loyal to her partner after Mason's death, and even agreed to marry him.

Sandeman no longer has a relationship with her parents, and Mason's grandparents, John and Sue Sandeman, who say Cindy failed her son.

"I did the best I could," Cindy said of her time with Mason.

"I’m a good person and honest and most importantly, a good mum."

John and Sue have tirelessly campaigned to ensure it is mandatory for childcare centres in Queensland to report on all suspected cases of child abuse - a step that may have saved Mason's life.

The legislation is due to come into effect on July 1, and will be known as Mason's Law.