2 examples here
London a few years back there was a pub across from our hotel that was recommended for the great food and atmosphere....they have a sign on the door, kids welcome until 6pm after that no one admitted under 18....makes sense to me and what was interesting was the pub had 2 distinct clientele and did very well as a result.
Other example in the great State of Texas last March. Our teenage son was allowed into the bar and he was also allowed to have a beer as he was in our presence. Seems that even though the drinking age is 21 in Texas they have a personal responsibility law which states;
Texas law permits service to minors (any age under 21) as follows: if the minor is in the visible presence of an adult parent, guardian, or spouse or other adult to whom he has been committed by a court
Makes sense to me. We asked the bar staff about it and they said they have never encountered any problems with this. The kid can't order the drink the parent has to and the parent has to remain on the premises.
Big difference between bars and nightclubs signs at the entrance to nightclubs clearly indicate no minors.
So the option is there for the bar owner to decide and in the case of the London bar they split it down the middle.
Wonder how this will change the restrictions on beer tents at outdoor events....