Family of 4 (2 adults, 2kids (15&7)) travelling to Washington for 4 days, followed by 4days in Boston and 4days in NYC. We are looking for attraction suggestions suited for all of the family. We are interested in culture, shopping (we heard that clothing is tax free?) and anything else that is suggested, because we don't know much about the area. Also, what is the costs of food and the attractions whilst here please?