For the couple months I have been eating off the kids menu when I go out to eat and I have found it to be very beneficial for the most part. From dine in restaurants to fast food getting the kids meal means smaller portions and smaller prices. I have found I can be satisfied by the the smaller sized portions. Typically the "kid size" portion is the correct portion size for anyone. The adult size portion is usually enough for 2-3 meals depending on what you order and what restaurant it is. I started doing this when I had to go to a business meeting and I just didn't want all that food. I saw that the menu said for kids of all ages so I gave it a whirl. I ordered the kids grilled chicken sandwich with baked beans. The portion was perfect and it was only 3.50 and included my drink! From that point on I payed close attention to all kids menus when eating out.
1) Some places do have age limits, however I have found A LOT of them do not, or will bend the rules.
2) Some restaurants only offer pretty unhealthy foods on the kids menu but many restaurants will substitute the fries for broccoli, coleslaw, or a garden salad. Also, many restaurants are trying harder to offer healthier kids fare.
So, this will not work every time you go out but I would say I do it at least half the time and I am a big fan. Just a tip. I am about to eat my teriyaki kids meal from Pei Wei: Grilled Chicken, Veggies, and Brown Rice in a yummy sauce. Half the price, half the calories, all of what I need for lunch.