Fiji. It's a 3-4 hour flight from Sydney. Most resorts on the coral coast have a deal where kids stay eat and play for free (1 child per adult) as well as do deals where adults can have there accommodation meals and drinks included - naviti, hideaway and outrigger resorts are 3 that I have been to. They all have kids club to.

My advice tho search for flights that leave Sydney (or ur closest airport) early in morning so as to get a good first day in and ones that leave ur holiday place late in the night/afternoon so ur not leaving the resorts in the early hours of the morning (eg 3am)

- don't tell kids that ur going on a plane, particularly if they stress easy. My parents never told us where we were going or how we were getting there. They day before it was 'going on holidays tomorrow, pack swimmers and summer gear'