An appeal will be launched into the sentence of the man jailed for killing Katherine Leadbetter and her partner Matthew Field when he struck them with a stolen car last year, Attorney-General Shannon Fentiman says.

In January last year, a 17-year-old under the influence of drugs and alcohol was driving a four-wheel-drive in Alexandra Hills when it collided with a tow truck, causing it to roll and strike the couple.

They died at the scene and their unborn son Miles was delivered stillborn shortly after.

The now 18-year-old man — who cannot be named as he was convicted as a juvenile — was handed a 10-year sentence last Tuesday for more than a dozen charges including two counts of manslaughter.

However, after considering the teen's early guilty plea, his steps toward rehabilitation, and "genuine remorse and shame", the judge ordered he should be released from custody after serving six years.

The ruling was labelled "grossly inadequate" by the victims' families and a petition created by the Opposition to appeal the sentence has garnered more than 46,000 signatures.

Ms Fentiman said she had informed the families an appeal will be launched by the Office of the Director of Public Prosecutions this afternoon.

"There is now not much more I can say as the matter is before the Court of Appeal, but I can confirm that the grounds of appeal that the sentence for manslaughter was manifestly inadequate, particularly as the judge had determined that the offence was a heinous offence," Ms Fentiman said.

"I do again want to pay tribute to the families of Matt and Kate and acknowledge what they have been through and the community's frustration and anger about this case.

"I have listened. I have taken the advice from the Director of Public Prosecutions and now I am appealing this matter."

'I completely understand the community's anger'

Ms Fentiman said the Field and Leadbetter families were incredibly emotional when informed of the appeal and she had extended her support to them.

She acknowledged the backlash from the community to the sentence.

"We have lost the lives of two young Queenslanders and their unborn baby. I completely understand the community's anger and frustration," she said.

"I want to remind the community that this case actually prompted huge changes to our Youth Justice Act, the Youth Justice Minister has made significant changes to the Youth Justice Act and those changes are working."

State LNP Opposition Leader David Crisafulli welcomed the news of the appeal.

"This is a win for their families. They have gone through what no-one should ever have to. This is also a win for people power," he tweeted.

In a joint statement released last week, the families of Ms Leadbetter and Mr Field said the six-year jail term fell short of what the community expected, and they were serving their own "life sentence".