I can see this rule becoming more popular in more UPSCALE restaurants allowing no children under a certain age limit, but it would probably be going too far if they did it at more family friendly restaurants (someone mentioned IHOP earlier..). If they limit too many restaurants (family friendly) then there would be not as much family dining in public, which would be kind of disappointing to families who deserve a treat every once in a while. But I definitely agree with enforcing this rule at more upscale restaurants..
But if parents are going to take their kids out to eat, they need to be able to control them, and understand that they can't bring them to all these fancy restaurants and be ruining other people's dinners.