Chrissy,
Tangalooma is really nice. If you want to take them to the beach (just to look at least) Bribie Island is a nice little beach town not far from Caboolture. not too sure whats around that area, not much...really... its kinda half way from Bris and Sunshine Coast. What about Under Water World? that's about 30mins north of caboolture approx at Mooloolaba that's fun for kids... and also the Big Pineapple too is at sunshine coast