Like most large US cities, finding a public restroom, especially when you are traveling with children can be quite difficult. We have mapped the different locations we’ve found in our tour areas that are accessible to the public.
The city of Boston is to be applauded for the list they have put together -- which can be accessed here -- which we have included in our list. Many of these locations are fire / police departments or public libraries. We have noted in the descriptions which locations are from this city published list.
Hotels and restaurants are also good places for restrooms but most require that you be a customer so we haven’t included them on our map (there are a few that are on the City of Boston’s official public restroom list so we included those). However, when in need these are worth a try.