It depends on what you want to do--shopping, history, culture?
If you want to go shopping, you are right there at Copley Place, and a short walk from the Prudential Center and Newbury Street. Newbury Street has lovely shops, but tends to be expensive.
It's a short walk to Copley Square, where there might be a farmer's market (I don't know when they start). There's also Trinity Church, which you can tour. The Boston Public Library is right next door, and has a tour of the art and architecture of the old building.
From there, a short walk gets you to the Boston Public Garden and right beyond that is the Boston Common. I suspect the Swan Boats will be running for a ride around the little pond. The Boston Common is the start of the Freedom Trail, and several of the main historical sites in Boston are clustered within a few blocks.
You could take the subway to Faneuil Hall and Quincy Market--combination of history (Faneuil Hall) and shopping, with street buskers and lots to look at and plenty of places to eat.
There's a good aquarium on the waterfront with a nice penguin exhibit and a huge tank that you walk up and around. There's also the Science Museum in Cambridge, easily reachable by the T if you don't want to drive, and the Children's Museum in the Fort Point area, but that might be a little young for your group.
The Museum of Fine Arts is right on a trolley line and you should be able to find something that everyone likes there. Just a short walk from there is the Isabella Stewart Gardner Museum, which is an old private house turned museum that is full of the treasures Mrs. Gardener picked up on her many trips to Europe--not just paintings, but floors, walls, fireplaces, furniture, tapestries, china, figurines, you name it. It's a very eccentric collection, the building is beautiful with a stunning courtyard and I consider it a little hidden gem.
Somewhat expensive, but fun, is the Boston Duck Tour, where you ride an amphibious vehicle around Boston on a tour, and then splash into the Charles River.
Boston by Foot offers guided tours.
Unless you are really used to Boston driving, I'd recommend getting T passes and taking the subway most places. There's not a lot of parking and it is expensive. The T will get you pretty much everywhere you want to go. Check out the MBTA website--you can type in your address and the address of where you want to go, and you'll get a couple of alternate routes, with fares and maps and directions.