Honestly you need to be realistic about the holiday you choose with young children and lower your expectations, then a holiday with young children can be relaxing and enjoyable.
Go on the same kind of holiday you would have chosen as a childless couple with children under 5 and of course it will be stressful and a let down.
Cheap and cheerful with loads of space and children the same age running about is the way forward on holiday with children. Camping/ glamping / holiday farms, that kind of thing.
www.camping-bellaitalia.it/en/
www.harvestmoonholidays.com/our-treehouses/
www.tyrol.com/book-your-holiday/farm-holidays
We've done, and enjoyed, all the above with 3 children under 11 at the time of the holidays (the first one we've and enjoyed with 2 children 3 at the time and with 3 children all under 6 at the time, and met families with up to 8 children, and lots of families with several tinies).
We tend to do the Bella Italia style of holiday almost every year, though not that site specifically - there are cheaper smaller sites now we are confined to school holidays and need/ want three bedrooms due to children's ages.
Of course its not the law to go on holiday just because you can afford it, so yanbu obviously to decide not to until the children are older, but yabvu to think a holiday to Australia is a typical or easy choice for a family with two children under 5 - obviously its the high stress, high effort, high cost end of the scale and something cheaper and closer to home and less ambitious will be a million times more fun and less stressful for many families while children are small.