I think Antico Forno would be a good choice. Solid approachable food (great gnochi and chicken parm (when on the menu)) w/ a brick oven, loud enough and teens can get a pizza if they are so inclined. Cheaper than the most expensive places.
I second L'Osteria. Had lunch there today in fact. Best red sauce Italian "comfort" food in the North End IMO. Delicious, tender, and perfectly prepared Veal Parm with pasta for only $11.50. What's not to like?