Having grown up in the Madison area, I can attest to the kid appeal of Ella's Deli. It's a one-of-a-kind spectacle of a refreshingly analog kind in this era of Playstation 2 and Pixar. The interior of the restaurant is an amazing blurring, whirring, rolling, bobbing, circling motorized mayhem...in a GOOD way. Every child in the Madison area should be taken to Ella's Deli at least twice each year. Failure to comply should be actionable under Dane County's child welfare laws.
That said, the food at Ella's Deli ranges, for the most part, from OK to good, punctuated with a handful of greats. Their sandwiches are good, they have delicious old-style french toast, great shakes, and very good matzo ball soup. Also, service is good and the staff is very friendly; it's a family operation all the way. If you've eaten at a lot of delicatessens in New York City or Los Angeles and you have reasonably high standards, take all of my positive food-related assertions with more than a few grains of salt.
Though I'm not Jewish, some of my best friends are (I love saying that), and I would not deign to drag them there unless they had kids, or asked, "Where's the only real Jewish deli in town?" Also, on the family outing front, it's a lot cheaper than taking everyone to a first run movie and, well, everyone has to eat.