"If you keep your property in the UK and rent in Oz it won't feel like you are emigrating it will just feel like a big adventure which is essentially what
it is." I disagree. I think going on an adventure is going backpacking around australia and asia, or Europe, whatever floats your boat country-wise, working from place to place, taking in the area and not putting down roots. It's not, IMO, uprooting your family, leaving behind your support network and swapping one job and set of bills for another.
If you're living somewhere on borrowed time you cannot form strong supportive friendships, because you know that in two years time you'll have to leave them all behind again when the "adventure" ends.
Fwiw I think the benefit of living abroad should not be underestimated. I loved my time in SA and I would do it all again in a heartbeat. I didn't want to come back and I have never been so miserable in my life as I was when I came back to the UK. And if we were given the chance to move again I would go, without so much as a backward glance.
But that is me, and anyone who says "oh yes, go for it, fantastic opportunity, you'd be mad to not do it," has almost certainly never done it themselves. And if not, why not?
This isn't about regrets here. This isn't about the op saying "I'd love to go to Australia, but I'm scared because I'll be leaving behind my support network," and then being told she might regret not going. This is about the op not actually wanting to go, but being prepared to give it a chance in order to help fulfill her dh's dream, fantasy, wanderlust, whatever you like to call it, but actually not wanting to do it. She's not going to regret not going because she didn't want to go in the first place.
And not wanting to leave behind your support network is a very valid reason for not wanting to move 12000 miles around the world.
There are no guarantees you will make friends there.
There are no guarantees you will find supportive people there.
And being stuck in a foreign country on your own with a toddler can be very isolating indeed if you're used to having supportive family around the corner.
We've recently moved 120 miles away from my support network, and even though it was my choice to do so it can still be isolating. But I know that in the event of an emergency I could get on the phone to my mil or my mum and one of them could, and would, be here within a matter of hours. You won't have that choice if you're 12000 miles away from your family. My ds is older now so it's much less of an issue, but I pulled out of a move when he was two because the thought of moving somewhere with a two year old and being totally isolated was terrifying. Toddler groups are great, but it can be much more isolating when they're tiny than when they're older.