Will , there are literally dozens ranging from the likes of Monkey World and Bovington Tank museum to the sandy beaches of Poole harbour (Sandbanks & Studland), Bournemouth, Weymouth and Swanage. There is the Swanage steam railway which runs from Swanage to nearly Wareham. There is a firework display and entertainment every Thursday night on Poole Quayand it is a good family atmosphere. The west of the county is mainly pebble beaches. Go to www.resort-guide.co.uk and select Dorset.
If there is anything further you want to know, possibly about a particular site, then just ask.