I second Aceman’s recommendation.
We’ve got a 2 yo and we’ve gone to all three over the last year.
Fiji is more expensive and will involve extra travel once you’re there unless you stay at Denarau. Beyond a village visit and water sports/activities there’s not much to do. They are great with kids but babysitting is more expensive and a lot of the kids clubs make you take your kids back over lunch time which breaks up your day.
Bali has a lot more activities, a lot more accommodation options, is cheaper and babysitting is cheap as.
Queensland is closer and more convenient to get to but more expensive.