Labour MP Jacinda Ardern has laughed off comments suggesting she isn't qualified to speak on paid parental leave because she doesn't have children.

The accusation was made by National Party backbencher Maggie Barry in Parliament last night during debate on a bill to extend paid parental leave to 26 weeks.

The Labour member's bill passed 60-61 despite National's opposition.

Ardern said she was more worried about Government opposition to the bill than comments made about her.

"I'm not going to lose sleep over it."

Politicians were often called to speak on things they didn't know a lot about, she said.

"I always try and fall back on research and evidence to fall back on when I don't have personal experience."

The comment was a jibe from across the House and Ardern said she tried to refrain from making personal references.

"You just never know their circumstances, but not everyone else follows that rule."

The comment also caused a barrage of attention on Twitter, particularly given Ardern's age - she is 32 today.

"I'd still like to think I'm relatively young but, even then, there's that question of whether or not we should be making personal comments like that."

During Ardern's speech in support of her colleague's bill, Barry interjected to ask "how many children do you have?".

Barry has a teenage son.

She declined to apologise following the debate.

- © Fairfax NZ News