i just toured australia in a campervan for a month with two kids...almost 4 yr and almost 2 yr.
in some ways, it was great... in others, it wasn't so...
first...
STAY AWAY FROM MAUI....go for APPOLLO, if you can. we rented a maui and although it was ok... i saw an appollo and it was MUCH better... more storage, nicer fittings etc.
second....
don't even consider it with a 4 berth. 6 berth is a MUST!
third...
if you can afford it, go for one that has a shower/toilet
in some ways, it was terrific. we didn't have to keep packing and unpacking as you would if you stayed in hotels. but the biggest problem was parking... finding a place to park if you wanted to tour the city was VERY, VERY VERY difficult. we didn't even try to see the sights in brisbane or melbourne. in sydney, we took public transportation all the time.
another thing to consider is this:
i, the mum, was the driver. the way the motorhome was set up, i had a "wall" behind me, as such, i couldn't see my kids nor hear them when they talked to me. my hubby had to be the go-between constantly. it was nerve-wracking to say the least. also, the motorhomes are quite noisy when you drive, they sound like you are in a tin can. so, even if i could have seen them, i still couldn't have hear them. the other problem is, if it rains, you are in a very confined space. there's no place for the kids to let loose.
with kids as young as mine, i would definitely do it again. but as i said, i'd book with appollo. i wouldn't do maui again.
good luck and have fun!