Where in Australia would you be moving to? Sydney is very different to Broken Hill.
We moved to Australia, shortly followed by my parents and then my brother. We are very fortunate to live within a few minutes of a each other and the kids enjoy a close relationship with my family because of this.
Before you decide what to do, you need to research the job, the true after tax salary, the true cost of living (Australia has the most expensive electricity in the world), health insurance (you will need this in Australia), the area where you will reside and schools. You are not guaranteed a spot at the school you are zoned for and I wouldn’t particularly recommend the local school either (this does vary area to area and state to state though). A large portion of parents privately educate, so the wait list at decent schools can be years long (although this depends on the city or town and quality and reputation of school you are applying to). Given it’s a niche position, I’m thinking it’s located in a more remote area and therefore no cafes on doorstep. Often the higher salary is a reflection of the remote location to try to lure people there.
If you are only planning to move for three years, you also need a return to UK plan in place, especially for your 7 year old who may miss their 11 plus exams and may not be offered a school place. Friends of ours who moved back after 5 years had issues with getting a School spot for their children even when they had a UK address as the LA refused to offer places when they were not yet resident back in the UK, even though they would have been at UK address they still owned, prior to the start of the school year. Instead their children now attend very expensive private schools.
I miss the UK and still call it home, even though my parents and brother are here. Without them, I think I would have struggled long term as I like being close to my family. We also struggled with “fitting in” - a lot of people (still cannot) understand what we’re saying or the meaning of what we’re saying and my husband is sick of being told he’s Irish. We mainly socialise with Brits because of this - but at least they can understand us!
Good luck with your decision - you may love it or hate it - but it’s an opportunity to experience somewhere else. If you do tell us where you’re thinking of moving, someone on here may be able to give you an idea if what the area is like.