All three frontbenchers were expecting their first children, with high hopes of balancing their parliamentary careers with young families. And for several years, this was the case, with O'Dwyer even welcoming her second child as a cabinet minister in 2017.

But both Labor MP Ellis and Liberal MP O'Dwyer have since announced they will leave politics at the next election, explaining they want to spend more time with their children, particularly as they reach primary school age.

Labor's Rishworth now has an announcement of her own to make: she and husband Tim Walker are expecting their second child in August.

"We're really, really excited," Rishworth says in her Canberra office. The baby will be a sibling for Percy, who is nearly four.

Rishworth concedes she was a little anxious about telling Bill Shorten she was pregnant, given the overlap with the upcoming election. But she reports the Labor leader was totally supportive.

"He was like, 'let me know what you need.'"

Rishworth, who is Labor's spokesperson on veterans' affairs and early childhood education, plans to work through the election and beyond. If the polls are correct, Rishworth will be a cabinet minister by the time the new baby is born.

"I still feel like I've got a lot to do here," she says.

Rishworth, who holds the outer-Adelaide seat of Kingston, is keen to emphasise that different arrangements work for different families.

"I really respect Kate and Kelly and they've made a significant contribution to this place," she said. "I have a lot of sympathy [for] and totally understand their decision."

As they did when Percy arrived, Walker plans to take a year of leave to care for the new baby.

"I feel luckier than other people out there that have to manage these things because my husband is able to take 12 months of unpaid leave and come and support me," Rishworth says.

The couple are also grateful to have both sets of grandparents on hand in Adelaide and rely on Percy's daycare as a "second family".

Rishworth says there are some aspects of political life that you can't change.

"People have said, 'maybe you should just give politicians 12 months maternity leave'. That's not part of the job. Part of your job is about being in there, whether it's your electorate or whether it's your role as a shadow minister or a minister. You can't just let things go for a long period of time," says the MP, who was first elected in 2007.

Rishworth's news comes amid discussion at Parliament House about how difficult it is to be both a parent and politician.

O'Dwyer shocked political watchers when she announced her retirement last month, explaining she had realised over Christmas how much she was missing of her children's lives. The Jobs Minister was soon followed by fellow government frontbencher Michael Keenan, who said he could not continue to be "an absent dad".

Similarly, last year, rising Labor star Tim Hammond quit during his first term because he was spending so much time away from his three young children.

Rishworth also acknowledges that time away from Percy is difficult.

"We decided that a routine back in Adelaide was better for my little one after that first year of travelling to Canberra," she says.

"It is really hard emotionally. I could say the same for men and women. You do feel guilty from time to time, spending so much time away ... you wouldn't be human not to feel that I think."

Rishworth adds it is important to note it's not just politicians who have to spend time away from their families.

"It is something faced by a lot of people that serve the country, such as our ADF personnel."

Beyond the option for partners to take parental leave, the trained psychologist says there is support that makes it easier for parents of young children in Parliament.

This includes the ability to breastfeed in the chamber or use a proxy vote if you're in the middle of a feed and can't make it to the floor of the House or Senate. Offices that can accommodate cots and family members are also important, as is access to the childcare centre in the building when the children are a bit older. She also cites allowances that enable family to travel to Canberra as important.

"I think that's the key. There are lots of personal choices, but it's increasing the options available."