Rights of the Child.
It's a pretty hefty document, with lots of fine print. It's possible that some provisions were unreasonably intrusive. And it's not like the U.S. is a major offender in how it treats its children.
If all the United Nations except Somalia and the U.S. have ratified this treaty, then it's painfully obvious that many nations on the list of ratifiers are largely ignoring the treaty anyway. Hypocricy is easy for some countries.