You can buy passes which will get you into Movieworld, Seaworld and Wet and wild. The passes vary in price depending if you want unlimited entry over 14, 5 or 3 days.
Dreamworld now also has a water park called white water world which is additional entry. All the parks have recently banned bringing your own food except baby food. I think so long as your not dragging an esky behind you your fine though. You should be able to get a family pass which is 2 adults and 2 children, under 3 is free at all parks.
Australia Zoo is about 2 hours north, just keep that in mind. All the theme parks are only about a 20-30 minute drive from Surfers and most hotels can organise bus transfers if you need them. I think any of the parks would be suitable for your kids.