Helen's Cafe on Main Street in Concord Center offers plain but family-friendly fare: plenty of burgers, salads, chicken tenders and the like.

Main Streets Cafe (also on Main Street - no surprise there) has delicious soups and salads for lunch and nice dinners, with an emphasis on New England fare.  You can crowd around one of their tiny tables, or sit at the counter and watch the bustling staff in action.

New London Pizza (thick-crust) and Sorrento's (thin crust) are both on Thoreau Street, and are both kid-friendly, too.  They're down the block from Dunkin Donuts and Starbucks, and right near Bedford Farms Ice Cream. 

Around the corner on Sudbury Road, you'll find Serafina.  It's a fairly pricey place, but hot dogs and hamburgers are available on their "bar menu" (which is also served at the table).  Chang An, also on Sudbury Road, offers reliable Chinese fare, with a good-value lunch buffet, plenty of booths, and some large-party tables.