The Queensland Art Gallery - Gallery of Modern Art runs a hugely successful program for 18mth - 3 year olds called Toddler Tuesday.
Each program focusses on one specific art work and runs for 2 months, 2 sessions a day on Tuesdays.
I have attended two programs with my children and have found both to be well designed for the target age group and most of all, fun.
The next Toddler Tuesday program runs from 5 August - 30 September 2008. Bookings are essential - 3840 7255.