It was delightful along the river and the museums we visited were quite interesting. There is a good walking tour with a free guide and the Mary Poppins connection is enjoyable for the children.
If you want a beach Hervey Bay is reasonably close and we visited a child friendly zoo. The water Park in Hervey Bay is excellent for kids.
Maryborough has many beautiful old Queenslander styled homes that have been restored and are truely lovely pieces of architecture.
There is also the old customs buildings and the churches.