I agree wholeheartedly with your post.
First, I took my daughter, now age 10, to a variety of restaurants and never once did I receive so much as a dirty look. I established with her early on the ground rules and my expectation that she follow said rules. I have a well behaved child now with a rather sophisticated palate. One of her favorite meals was at Spago in Beverly Hills at age 7.
Second, age has nothing to do with it. I see adults whose behavior is so unmannerly, so inappropriate and breath-takingly rude.
Restaurants should treat patrons on an individual basis. Toss the ones who are rotten, regardless of age, and welcome the opportunity to help shape the experience of well behaved children.
Going in with 4 we occasionally got a dirty look on the way in. At one Flamenco concert a woman seated near us made loud comments to her companion about how inconsiderate people were to bring children.
At the end of the performance she came up to us and said that she was so impressed with the children and how well they behaved had been. We thanked her without mentioning that her loud “Hola Jose” shouts throughout the performance had been distracting.