Please don't be sorry Tinks I have no idea about the worlds - haven't been there since I was a teenager. In the kids area is there a height/weight limit to the rides? I've never heard of white water world so I'm off to check that out too and I can't believe I didn't think of dreamworld - d'oh.
Thanks for your help Tinks.
There are height limits for the bigger rides at all parks. In Movie World's kids area there are only 2 rides with height limits, the roller coaster and the one next to it which I can't remember the name of. All the other rides are for all ages, your 2yo would be able to go on them no worrie, you can go on too. The 2 with height limits your 4yo would be able to go on.

I don't remember any height regs for the kids rides in Dreamworld apart from the Rugrats Rollercoaster which my 5yo loved but 4yo was too short to go on. Same with Seaworlds kids rides.

Not sure about weight limits, I don't think there are any. If you look at the various parks websites you can read all the rules and regulations for each ride.