Our flight in July to Cairns just got changed and we have a layover in Brisbane from 9:30 am to 3:30 pm. Does anybody have a good idea re what to do other than sit around the airport? We have a four year old in tow and would love him to run out of energy before the flight. (I'm sure other passengers would like that, too) Thanks!

Walk outside the terminal and get on the train into the city. Get off at Central and ask directions to the Queen Street mall, walk up the mall to the river and you can take a boat ride perhaps to Lone Pine ( depending on the times) or just window shop.

Take the train to Central (station) and walk to the river and catch a ferry to Southbank. It is across the river from the city. There is a 17 hectare park with paths, 3 childrens playgrounds and a beach that has lifesavers everyday of the year. There is a part for paddling which could be fun for the 4 yr old. They do talk about a childrens water play area being developed but not sure when this will be finished.
www.south-bank.net.au will give you an idea of the area.
There are ferries (river cats) that would also give you an idea of Brisbane and the river and would fill in time but may be a bit boring for a 4 yr old.
The waterfront park in Cairns has a childrens water play area and it looks great fun. We were there in May and even at dusk there were lots of families enjoying it. Have a wonderful time

Thanks so much! I especially appreciate the details of how to get there...both ideas sound great, so we'll decide depending on the weather and our energy level.

Just a note, I don't think they allow any left luggage at the airport so see if you can check in and get rid of your baggage straight away. Note that the international and domestic are separate but the train runs between the 2.
Get a day return ticket or see about a family deal ticket on the train as already suggested, gives nice views and very easy and the staff will give you tips where to get off etc.
Follow Jilly's tips, it's a nice place for the day !

Sorry and Jill ! depending where you are heading next there is good shopping in the mall and you can get great food at the outside cafes.

Thanks so much for the details. JillyF--thanks for the Cairns tip. We are leaving in a week,and my son has declared that "Australia is his favorite continent" (After Africa).