According to US Government statistics, there were an average of 6,000 to 7,000 minors who were apprehended crossing the United States and Mexico border unaccompanied by an adult between 2008 and 2011. These unaccompanied minors would be placed in custody with the Office of Refugee Resettlement.
In 2012, the number of unaccompanied children who were place with the Office of Refugee Resettlement increased to 13,625 minors.
In 2013, the number increased again to 24,668 minors.
These figures only include minors who were placed in the office, and does not include the children who were sent to Mexico in conjunction with its government.
Most of the children who end up at the office are from Central America.
Source: Associated Press, “Judge: US government assisting child smuggling,” Washington Post, December 19, 2013.