Even if you don't attend a Red Sox game, the tour of Fenway Park was fantastic! But my family loves to see all of the different stadiums around the US, especially if we can catch the SF Giants' away games! Being able to hang out in the dugouts, lockerrooms, press boxes, etc is a really neat experience.
Other things we did in Boston included walking a good portion of the Freedom Trail. Many sites along the way to see--Quincy Market, Paul Revere's house, etc. We also did a harbor boat tour. Really cool to see the skyline from the water. And you can get off halfway to see the USS Constitution up close. We took the subway in from our hotel in Cambridge a few times, and it was fine/safe.
Check out Trip Advisor and see what people have rated as the top attractions around town. That is my main way to get information about cities we are planning trips to. And Google Maps is a lifesaver when mapping out what order to do things in.
Have a great vacation!