A family day will be held Saturday from 11 a.m. to 6 p.m., with events at Choate Park, Cassidy Fields, and the Thayer Homestead, as part of the town’s tercentennial celebrations. The festivities will include musical performances, carnival games, vintage cars, a scavenger hunt, a dunk tank, square dancing, and a bike parade. In addition, organizers have rented bus “trolleys’’ for guided tours of historical sites throughout town, with narration provided by Medway Middle School students. Food and snacks will be available at “old-time prices,” organizers say, and the day will culminate with an ice cream sundae bar. For more information, visit www.medway300.com .