It is essential your date does not conflict with another local family event, sports grand finals or event where students may be involved away from school. The last thing you want is the risk of likely attendance opting for another event or leaving yours early to attend the other.
Weather and time are factors to consider. Cairns outdoor midday events are generally too hot and the first 4 months of the year you risk a 70% chance of unsuitable weather.
And remember , the sooner you book your amusement rides, the better chance you’ll have of getting the rides and date that suits you.