Are they getting enough sleep? How much exercise do they need? Are they spending too long in front of a screen?

This month, Australian academics launched a world-first app to guide parents to the 'just right' day for their children, helping them understand which combination of activities can best help mental, physical and academic outcomes.

Assessing data from 1685 children aged 11-12 from the Australian Child Health CheckPoint study, the Healthy Day App enables hypothetical adjustments to time-use behaviours to measure possible impact.

Simple measures like switching an hour of screen time for one of exercise could mean 4.2 per cent lower body fat, 2.5 per cent improved wellbeing and 0.9 per cent higher academic performance according to the app, which was developed by the University of South Australia and Murdoch Children's Research Institute.

"Because there's only 24 hours in every day, it's hard to fit everything in with the competing demands on our time," lead researcher Dot Dumuid told AAP, while rink-side at her daughter's early morning ice skating lesson.

"I wish we had the key - that would be awesome because everyone struggles with it.

"Parents do worry about getting all this right for their kids. And then, what your kids want to do and what they think is important may not match what you think is important or school thinks is important.

"The app is good to play around with for different ways to reallocate time and an estimate of how that is predicted to impact health."

As well as helping parents juggle relaxation time, homework and extracurricular commitments for their kids, getting the balance right now can make for better long term health prospects, lowering the chances of heart disease, obesity and diabetes, Dr Dumuid said.

"What our kids do with their time does affect a lot of things across their health.

"Some of that stuff is not felt now - like being a little bit on the overweight side but (the trouble can) start in childhood and be felt later in life - like diabetes or heart disease."

But despite the name of the app, the balance doesn't have to be spot on, on a daily basis.

Sometimes children - and adults - just have a quiet day with too much screen time and that's ok.

"There can be a balance over a week or over a month. Not every day has to be perfect," Dr Dumuid said.

"And while TV watching is usually always bad, some of the interactive games and web stuff they do are actually beneficial for academic performance.

"We want kids who are happy and adjusted."

Australian Associated Press