Children as young as 12 or 14 getting married is not at all common. The study the wikipedia article you posted claims less than 1500 hundred children over 18 years that were married at the age of 12-14 in a country of over 330million. It also points out that of those under 18, the vast majority was 17. Not to say that it isn't a problem and should be fixed, but its not common what so ever and I would guess 90% of americans will never meet someone married under the age of 18 and except for some of the most rural middle of now where places its considered pretty horrific and unacceptable by most americans.