When my nieces and nephews (ages 3-13) come to visit, these are BIG hits:
Barking Crab: 88 Sleeper Street, Boston. Fun because it's on the water. Good food. Neat place, especially at night.
Bertuccis (as mentioned previously!): all over.
Cheesecake Factory: in the Prudential. Yeah, it's a chain restaurant but it's a good chain restaurant.
RedBonez: 55 Chester Street, Somerville. Really good BBQ, really kid friendly. Close enough to Cambridge I forget it's in Somerville.
Stockyard: 135 Market Street, Brighton. Family-oriented steakhouse. Almost an institution.
Zaftigs Deli: 335 Harvard Street, Brookline. Great food! Great atmosphere. This is my favorite deli in the entire area.