The Queensland Museum is 150 years old and the South Bank site has just been extensively renovated.

It has some fantastic features for kids now – all free.  The new Discovery Centre is particularly good for kids:

Hands on exhibits for the kids - Discovery Centre
Phasmatodea (Stick Insects) in a glass case for the kids to see. These things are huge - 50cm long
MicroEye Projection Microscopes - great fun for kids
Butterflies Display
Renovations - new staircases
Beetles - Discovery Centre & main Qld Museum collection
From Little Things, Big Things Grow exhibit - Qld Museum