Green tree frogs are probably the best known of all Australian Frogs. They are easy to look after, long lived and kid friendly. You don't need a lot of space and feeding them is simple.
A good size glass terrarium is 60x60x45cm with a soft mesh top and swinging door to make feeding easier. They like to be kept around 25-29oC. This can be best achieved by heating their water with an aquarium heater. A good substrate to use is artificial turf, it can be taken out washed and replaced when dry.
Water needs to be fresh and clean all the time. You can use a fish tank neutraliser to remove chlorine from tap water to make it safe it use. The water should be partially changed often to keep it fresh.
Frogs love live crickets and woodies as well as worms. Calcium powder should be dusted on the insects every other feed and vitamins once a week. This will keep the frogs from becoming calcium deficient. They love their food and will cram it in their mouths when you offer it up.