Haven't done it with DCs, but travelled up and down the Eastern coast of Australia in one with a girlfriend many years ago. It was fantastic, and something I'd love to do again with the DCs.
The van we had was lovely, fairly expensive iirc, more than travelling and staying in youth hostels but probably a lot less than hiring a car and staying in hotels. It was roomy enough, plus we bought a cheap tent to pitch outside (for privacy when BFs aussie man travelled with us for a week or so) TBH, we could probably have got it cheaper if we'd booked before we came, but this was preinternet for us and we hadn't decided whether to hire or buy.
Australia's pretty well set up for this kind of thing though, From chatting to other campers it seems to be the thing to do when you retire - buy a motorhome and just follow the coast. The sites were really well set up (at the time far better than some UK ones are now) and many of them are in towns. We rarely stayed anywhere that wasn't in town, or wasn't served by public transport so you could easily get into town (the odd times we stayed in inaccessible places it was by choice)
There were a surprising amount of families, even though we were there in winter (June/July/August), and most places had children's facilities.
I loved it, I would honestly say it was the best holiday I've ever had (and that's including the fact that some fairly nasty personal stuff happened whilst we were there - I spent the last three weeks on my own!) I would be there in a flash if I could, even with the DCs
Costwise... it's difficult, I know we spent around £4k in 12 weeks, but that was hiring the van, petrol (drove from Sydney to Melbourne up to Cairns and back to Sydney), flying to Alice Springs and back, BF flying from Proserpine (I think) to Sydney, site costs, eating out pretty much all the time and large amounts of alcohol. It was a fair few years ago too.