My nephew and niece love the Horrible Histories tv show and I found this wich should be a hit with primary school age children. Horrible Histories The Exhibition www.anmm.gov.au/whats-on/exhibitions/on-now/horrible-histories Adults $30, Child (under 4) FREE Child (aged 4–15) $18 Concession $18 Family $75 Members FREE
Ice Age Live on Ice an amazing show to treat the kids with these the holidays. Sydney Olympic Park 15th April - 17th April $40 - $172 www.iceagelive.com
I'd recommend taking the kids on a day trip or tour of the Blue Mountains. The Scenic Skyway cablecar (http://www.scenicworld.com.au/), Jenolan Caves and Featherdale Wildlife Park are must-see highlights.