took our 2 yr old and 4yr old about 7 years ago and they had a blast.. just seeing the place,on the beach,zoo in sydney,trips on a boat around the harbour,flying on the plane.sydney opera house.driving from brisbane to sydney,forests,if u are driving u may be lucky to see a kangaroo etc on the roadyou name it and they enjoyed it.
just make sure they get plenty of sleep and take them weverywhere the ozzie cater for kids in a big way,every beach almost has a play area and a bar bq area..one big adventure