Thanks so much for all the replies!
For sure we are going to walk at least part of the Freedom Trail. Since we all love Harry Potter, it will be a bonus going to the Science Museum. I am wondering if trying to go to the Aquarium the same day will be too much.
The people we are visiting are invited to a private party, so Boston's First Night may be the way to go for us.
I did not know about the Holocaust memorial, so we will add it to our list.
Now I just need the New England weather to behave itself.