Plenty to see and do.
Port Arthur: A special place to live and the guides have some great stories to tell. If the kids miss behave lock them in the solitary confinement cells for a few minutes and they will be good for the rest of the day
Cadbury Factory: You can do a tour of the factory which may be a little boring for you but kids seem to love it and it is interesting.
Tahune Airwalk: Walk 100 meters up in the air amongst the trees. It is very safe but you do have to like heights!
Taste of Tasmania and Salamanca markets: In the summer around Salamanca there is the "Taste" which is like a food fair with lots to see and do plus the Sydney to Hobart boats will be around wich adds to the atmosphere around the docks. Also the kids will have a good time at the markets
Cascade Factory: Sure the kid’s can’t drink the beer but they do also make fruit drinks and the tour is a great thing to do. Make sure you book ahead as the tours fill up quickly also from there you can drive up to Mt Wellington which is amazing.
You will have a great time. Enjoy