Dinner at North End
There are a lot of threads on the North End, which can be easily accessed by searching. In addition, 'reasonable' price is very much in the eye of the beholder...so being more specific will allow greater help from posters.
I will start, however, by saying that pizza at Pizzeria Regina is reasonably priced by almost all standards, it's family friendly (ish) and very good food. Best seafood is probably Neptune Oyster, but it's lack of reservation policy, and small space generally preclude it being good for families in general.
63 Salem St Ste 1, Boston, MA 02113