As far as I know, they don't do the Cadbury tours anymore, as in they don't let you in the working factory like they used to
They still have the shop, and they have an information movie type thing in there you can opt to see. I'm not sure if it's still applicable, but they used to insist on closed in shoes to even set foot in the door due to OH&S regulations (so no thongs or open toed shoes). That might not be an issue now the tours no longer happen, but something to consider as it would be painful to get there and find out you can't go in.
Also, even though there is no tour, they still charge you to get in. You can see more here
As for the rest of Tassie, Salamanca markets is a must see, Tasmazia is another that the kids will love, Boat Harbour Beach is well worth a look even though they've now closed down the only shop there - there may be a kiosk running over summer but no guarantees, the Stanley Nut and Highfield house in Stanley is worth a trip, Grindlewald near Launceston is lots of fun especially if the weather is nice (mini golf for the kids, a jumping pillow and water activities), there is an excellent Mine Muesum at Beaconsfield particularly designed for kids, Queen Victoria museum in Launceston is great for kids (and free), Mona in Hobart is great for adults but I don't think my kids would enjoy most of that, the Maker's workshop in Burnie is worth a trip especially in school holidays when artists are doing workshops that kids can be involved with, the aquatic centres in Launceston and Hobart are lots of fun, and there is the Wonders of Wynyard in Wynyard (on the NW Coast) where you can get information about the Tommeginner people who were the traditional custodians of the NW Coast as well as see a big collection of antique cars.