The family of a young couple who were expecting their first child and were mowed down while they walked their dogs, say all they have is an unfinished baby blanket to remember them by.

Kate Leadbetter, 31, and her partner Matthew Field, 37, were overjoyed to soon meet their first child, a son named Miles.

However, tragedy struck when the pair were run over in Alexandra Hills in eastern Brisbane on Australia Day.

A 17-year-old has been charged for allegedly hitting the pair with a stolen Land Cruiser while high on drugs, and on bail for 50 other charges.

He has been charged with murder and several other crimes, including ramming another car hours before.

Kate's mother Jeannie and stepfather Tom Richter said Miles would have been their first grandchild.

He was due to be born in May.

Sadly, the tiny crocheted blanket will remain unused by baby Miles, however it has offered the family a tiny bit of hope amid their heartache.

She vowed to finish the blanket in honour of her grandson, telling Courier Mail: “I haven’t gotten back to it, but I will. I will do it.”

Since January 26, the grieving parents' say their lives have completely changed and everything they do has a “hollow ring to it” and they just “go through the motions.”

Jeannie said that during Christmas, just a month before their deaths, Katie had declared how big the family would be the next year once little Miles arrived.

“I should be like, "wow, now is five weeks 'til the baby is born… I should be worrying if I'm capable of looking after a newborn overnight, or if I've lost the skill". I thought (that's what) I'd be worrying about right now,” she said.

'We had the best life. We were just sweet, it was all good. And then in the space of thirty seconds it just stopped…

“We had a great kid and she had a great partner and we finally had that cool bit of playing with "grandies" to look forward to.”

Mr Richter relived the moment when the couple told their family they were pregnant, saying they had looked overjoyed.

He said they came over and Jeannie opened a bottle of wine, but Katie turned it down before telling them the news, with all four of them bursting into tears.

Tragically, just months later, their world would be completely shattered when local police officers knocked on their door.

The parents said they were in “disbelief” that they could be gone because the odds of what happened were “infinitely small”.

The two dogs survived, which to Richter showed how it was just a matter of seconds difference between them surviving or not.

On Wednesday, Mr Richter will release a song titled “Three Hearts” to remember their loved ones who were tragically killed.

“Every time we think of things we want to tell Katie, even just silly little things we want to tell her, we can't anymore. Our beautiful daughter isn't there,” he said.

Kate and Matt died at the scene on Finucane Road in Alexandra Hills.

The teen allegedly fled the scene before stealing a set of keys from a nearby house.

Money from the download sales of “Three Hearts” will go towards the pair’s memorial.

Donations to Queensland Homicide Victims Support Group have been encouraged.