These are really neat places. Michigan City is very close to Chicago if you would want to visit the aquarium. Grand Haven is close to Saugatauk, another nice little town but more of an artist colony. My grandkids, including the triplets now 6, love St. Joe. Every year they have a 'theme' and there are statues around town. One year dogs, one year zoo animals, etc. They also have a Curious Kids Museum that is absolutely awesome - although your guys may be a little young. Great splash pad! The pizza place on the beach is great along with a unique toy store downtown and fun ice cream shops. You might check our some old copies of Midwest Living as they often feature one of these neat towns.