If carpool lanes are reserved to encourage people to commute together and as a result have fewer drivers on the road, shouldn't the number of people needed for the carpool lane include licensed drivers only?
How are you going to determine if everyone in a car is a legal driver, even if they are all of age? Stopping every car to check IDs would defeat one purpose of the lanes which is to reduce the time it takes to get to work. Not to mention it would probably not be legal to check every ID without probable cause anyway.