I'd rather kids come to restaurants when they're old enough to understand the concept of sitting still. Maybe my parents had an iron fist or something, but from at least 6-7 years old I understood the concept of behaving and sitting quietly. Granted I hated going to nice restaurants as a kid.
Any younger than that and we just didn't go out to eat all that often that I'd remember it. Probably just kept to Perkins/Dennys type places. They're a bit like Wal-Mart - if you DON'T hear a kid crying somewhere, you wonder what's wrong.