A good question.
A local answer.

Check the airport transfer's current schedule and keep a firm turnaround time; a river ride may take longer than a simple walk and meal.

Check current event listings for your dates. A local performance or market can make an evening more distinctive than another long drive.

Confirm which service is free or paid today; older forum references to routes and fares may no longer apply.

Ask the hotel whether its fee covers a 24-hour period, the overnight stay or a fixed entry-and-exit window.

Check the last train or bus for your exact date before deciding to leave the car behind.

Explore a food market or neighbourhood dining street and compare current menus before choosing a place.

Check restaurant kitchens near your hotel for that Sunday and reserve a realistic arrival time after airport transfer.

Build days around a playground, shaded park or riverfront walk, then add one short paid attraction if it suits your child.

Combine South Bank's riverside paths with one nearby gallery, garden or café stop rather than leaving the city every day.

Choose the closer option if you value a relaxed visit and time for Brisbane itself; choose a larger park if its full-day exhibits are the goal.

Look at the current forecast and water conditions close to the date. Air temperature alone does not tell you how comfortable swimming will feel.

If the buffer works, focus on South Bank or one river-ferry segment near a direct airport return route.