Northfield itself doesn't have a lot other than the strip mall where the Happ Inn is. Northbrook is going further north; if you're going as far as Max & Benny's, I'd also suggest George's What's Cooking on the "Deerfield" side of Waukegan Rd.
George's What's Cooking - Greek/Jewish diner/deli. Large portions, friendly service, decent if not inspired food, great for all ages
350 South Waukegan Road
Deerfield, IL
Or, you can head a little bit west, to Glenview:
Sweet Tomatoes - great family place - salad bar, pasta bar, potato bar, etc. It's a chain but I always find something to like there.
2351 Willow Rd
Glenview, IL
Walker Brothers - pancakes and brunchy food all day - but this location doesn't serve sandwiches or non-breakfast food
1615 Waukegan Rd.
Glenview, IL
If you head a little bit east and south, Wilmette has options such as:
Akai Hana - standard Japanese sushi place, very family friendly (close to the highway at Lake St and Skokie Blvd.)
3223 Lake Avenue
Wilmette, IL
Olive Oil - I have several friends who swear by this place - haven't eaten there myself but worth a try. Mediterranean cooking, soups, salads, sandwiches. It's in downtown Wilmette very close to the train station.
1154 Central Ave
Wilmette IL, 60091
Ridgeview Grill - a step above a standard diner; overall decent, fresh, breakfast until 4 pm plus soup, sandwiches, etc. Location on Lake St. and Ridge Rd. intersection.
827 Ridge Rd.
Wilmette, IL
Walker Brothers, same menu as mentioned above. This location is in southern Wilmette on Green Bay.
153 Green Bay Rd.
Wilmette, IL
"You should eat!"