Labor's finance spokeswoman Katy Gallagher said the comment was insensitive and hurtful to parents and children with a disability.
"As the parent of a wonderful daughter with autism, I was really upset by that comment. I found it really offensive and quite shocking," Senator Gallagher told the Seven Network.
"People who have a disability, children with autism, it is a kind of response they get all the time that people are blessed not to have what they have when in actual fact, every child is a blessing."
The comments from Prime Minister Scott Morrison show a lack of connection with everyday people, Senator Gallagher said.
"It may be a clumsy comment but they still are insensitive comments and can offend people. Maybe he can front up today and explain what he meant by that," she told Sky News.
"Part of the battle we are up against is that our children are less or not as good as others and that simply isn't the case."
Finance Minister Simon Birmingham defended the prime minister, saying the comments were in relation to not having to deal with the complicated National Disability Insurance Scheme bureaucracy.
"The prime minister actually in that context was talking about the not having to deal with the many challenges of systems that you have to work through to get the support," Senator Birmingham told the ABC.
"I think he was expressing the type of sentiment many Australians would understand."
Liberal senator Hollie Hughes, who has a son with autism, also defended the prime minister's comments.
"To be honest, I did not think of anything of them at all. I certainly didn't take anything negative away from it," she told the ABC.
Senator Hughes says the anger has been misplaced by people who are against Mr Morrison.
"I know there were days, very early on when my son was younger, that were really, really hard. I didn't feel particularly blessed.
"We have a much higher suicide rate within the autism population. We have a higher unemployment rate than the general disability population. There are issues we can be angry about."
Mr Morrison will continue his campaign in Brisbane on Thursday following the leaders' debate, spruiking a plan to make life easier for Australians in outer suburbs.
The government will provide $28.2 million for 66 successful projects to address mobile phone blackspots across the country and a further $78.5 million for projects that address mobile phone and connectivity issues in outer urban and urban fringe areas.
"Investing in digital infrastructure is all part of our plan to make Australia a top ten data and digital economy by 2030, helping to grow businesses and jobs, while also providing Australians with better access to essential services," he said.
Meanwhile, Opposition Leader Anthony Albanese is travelling to the NSW South Coast to the electorate of Gilmore after claiming a narrow win from the first leaders' debate.
During Wednesday night's televised debate, Mr Albanese won more of the support from the group of 100 undecided voters.
Mr Albanese received 40 per cent of the vote, compared with 35 per cent for Mr Morrison, as 25 per cent of the crowd remained undecided.
The two leaders traded blows over stances on boat turnbacks after Mr Morrison accused the Opposition leader of being inconsistent on the issue.
Both leaders received questions from the audience on a federal integrity commission, support for small business, and housing affordability, as well as trust in politics.