When are you going to give your child a brother or a sister? Aren't they lonely? What happens if they die and you are left with no kids?

Parents of only children by choice are no strangers to these questions.

But evidence shows there are very few drawbacks to a one-child family, and according to one expert those passing judgement are likely envious because they have "suffered through" raising several children.

Between Canditta Natakuapa and her husband, they have 17 siblings. So deciding to have just the one child was easy for the pair who value work-life balance and giving their son "the best start in life".

The Brisbane business owner is dedicated to her work and said having multiple children would interfere with that.

Professor Toni Falbo says maintaining a career and giving a child a good education were key reasons to have just one. ( Supplied: Pexels )

"I get a lot of enjoyment out of my job, so I think for me personally having a happy work life gives me a much better balanced home life for my son, Gabriel," the 35-year-old said.

"By having only one child we can afford better schools, without sacrificing something else."

Having a one-child family has also given Canditta and her husband more freedom and flexibility.

"Gabriel does swimming lessons and he's about to do little athletics. If we did choose to have multiple children and they had different interests we would have to split up on the weekends to accommodate that," she said.

"Recently we had a wedding in Melbourne and it was much easier for us to hop on a plane and fly down. The family with four kids, they had to do a road trip because of cost — four kids in a car, I wouldn't want to do that."

But despite feeling fulfilled by their family unit, Canditta often faces judgement from other parents.

"I've copped comments about being selfish for not giving Gabe a sibling," she said.

"My son has more than 20 cousins … it's not like he's missing out on people to play with.

"People have asked what if we died and Gabe would be left with no immediate family — that was a real shock to me.

"At day care my son was showing off his new shoes, and another mother said to me, 'Well you can afford to buy your kid the world when you only have one'."

That kind of resentment is no surprise to Professor Toni Falbo from the University of Texas, who has spent more than three decades researching single-child families.

She is about to undertake research into whether mothers of one child are seen negatively by people who have "suffered through the experience of bringing up several children".

"I am hypothesising that yes … they may be outraged that a one-child mother is not making a similar sacrifice," Dr Falbo said.

Only children aren't lonely, expert says

Dr Falbo said pressure from society to have more than one child was likely based on "deep-seated and probably unconscious biases within the human mind", that by having at least two children the human race increased rather than declined.

But environment was also a motivation for parents choosing a one-child family, she said.

"Nowadays, there may be more couples who worry about climate change and decide that one child is their way of making a contribution to reducing global warming," she said.

She said benefits included the child having more attention from their parents, and mum and dad being able to enjoy activities without the stress of additional children.

There was a potential downside to having an only child, Dr Falbo said, but loneliness wasn't it.

"The drawbacks involve the risk of losing that child, a young death for example, and then [the parents] have no children," he said.

"But my research in China and the US indicates that only children are no more lonely than those with siblings … because most parents with one child promote peer interactions."

Canditta agreed there was a fear of losing her son, that she was "putting all her eggs in one basket", but conceded the fear would be the same if she had two or three children.

'I want my child to have the same opportunities I did'

Mother-of-one Lorrie Brook went through IVF with her husband to have her daughter Tehya, now four years old.

Lorrie Brook had just one child to ensure she had the best opportunities in life. ( Supplied: Lorrie Brook )

An only child herself, Lorrie was keen to stop there and give Tehya the same opportunity.

"I know that I got given a lot of opportunities from my parents that if I wasn't an only child I wouldn't have had," Lorrie, 34, said.

They included education benefits like an exchange trip to Japan and enriched extracurricular activities.

Lorrie said the main positive to a one-child family had been "the obvious — childcare fees".

"I don't know how people afford to put more than one child in day care," she said.

"It costs us $450 a fortnight."

Lorrie said the only pitfall was leaving her daughter behind without siblings. ( Supplied: Lorrie Brook )

Routine and work-life balance has also been easier to maintain.

"My husband is a shift worker so being able to spend time with him when he's not working while still making sure Tehya is doing the activities she's involved in has been really important," she said.

Lorrie said the only foreseeable pitfall was leaving her daughter behind without siblings.

"From my experiences as an only child I know that at this point in my life if I lose my parents it will be very difficult because I am so close to them," she said.

"It's probably the biggest thing that's played on my mind."