Brunch near Walnut Street Theatre?
I agree that Jones would be good for kids. Never had brunch there, but imagine it would be good.
Another option would be the recently opened cafe at Talula's Garden. (208 W. Washington Square) There are a bunch of tables, but I think you order from one of two counters with chalkboard menus, rather than being waited on. I got there very early one morning before work, and they had just put out a beautiful looking frittata. I had a lemon scone that was outstanding, and I'm not even a big scone fan.
There's also a Pain Quotidien near the Walnut Street Theatre.