This comes from the UN convention on rights of the child. (http://www.unicef.org/crc/index_30177.html)
America, along with Somalia and South Sudan, has not ratified the convention.
(https://en.wikipedia.org/wiki/US_ratification_of_the_Convent...)
I don't know much about law, but I am a fierce advocate of state rights based mostly on the idea that it is far more feasible to have a democratic government that involves millions or tens of millions than one that involves hundreds of millions. This issue is however one place where my ideas trip up. It is kind of embarrassing that we are 1 of 3 (assuming the grandparent comment is correct) countries not to ratify the treaty and the other two are an (essentially) failed state and a brand new one that has to sort its internal self out before working on such things as UN treaties.