Hi Rob, we went to Dreamworld last year with a 1,6 and 8 year old and we had a ball. You can spend all day there and its surroundings are great. There wasn't much in the food catagory - I think you can have a buffet lunch if you book, they had KFC and a few small stalls with corn on the cob ETC. They also had a snow world which is about 100bt extra and you can tabbogan down a hill. We intend going again this year. There are rides for all ages.
We also went to Safari World in Bangkok. This is a lot like Seaworld on the Gold Coast. It has a dolphin show, 2 others shows ( hard to describe - like a James Bond action show and a Western show - a bit like movie world) . There are also a zoo there. You catch a bus around the park and see elephants,giraffes,lions bears etc. We didn't see all of it as it rained but they have a monkey show ( I think), birds, we had to leave as the rained practically closed it down so we will be doing this again.
Both were great and fairly cheap compared to our standards.

Hope this helps

Karin