That's usually not the case in the US. It depends on the jurisdiction, but bars can oftentimes be fined for underage drinking if a minor is on the premises, even if he/she isn't actually drinking.
Even in situations in which the venues have discretion (eg, nightclubs, comedy clubs), venues often don't allow underage patrons to enter, because they know they're going to make no money off of them, and they're just taking up space that could instead be going to a paying customer.
That's usually not the case in the US. It depends on the jurisdiction, but bars can oftentimes be fined for underage drinking if a minor is on the premises, even if he/she isn't actually drinking.
Even in situations in which the venues have discretion (eg, nightclubs, comedy clubs), venues often don't allow underage patrons to enter, because they know they're going to make no money off of them, and they're just taking up space that could instead be going to a paying customer.