WASHINGTON - Every day, 80 to 120 children cross the Texas border illegally - and alone.

What's happening in Texas reflects a nationwide trend: Immigration by undocumented children under 18 is on the rise, even as fewer adults come into the country illegally.

The Border Patrol apprehended 24,481 unaccompanied children in 2012, more than three times than in 2008. Of that total, federal authorities referred a record 13,625 children to another part of the federal government, called the Office of Refugee Resettlement (ORR) within U.S. Health and Human Services. This agency is responsible for the care and custody of minor children while their immigration status is considered.

These children, most of them teenagers, are temporarily cared for by the federal government in shelters and group homes in more than a dozen states, including Texas, Illinois, Arizona, California, Florida, New York and Virginia. The federal government foots the bill, but states feel the impact. Last year, Republican Gov. Rick Perry of Texas called the surge of children crossing the border a "humanitarian crisis."

The remaining 10,000-plus children caught at the border last year were mostly from Mexico, and many were sent home.

Most of the children who remain in U.S. custody are from Guatemala, El Salvador and Honduras. Many say they are fleeing violence from gangs and drug cartels as well as abuse, sometimes by their own family members. Others are trying to break free from poverty and get a better life in the United States, or to reunite with family members already in the states. In many cases, they crossed mountains and deserts, often relying on "coyotes," or guides, to get to the United States.

Whatever the reason, the increase has been so dramatic that it caught the government and advocates by surprise. In a typical year, federal authorities handled between 7,000 and 8,000 unaccompanied children. The total was 13,625 in 2012. By government estimates, it could climb to nearly 24,000 within the next year.

Providing temporary shelter and support services to these children while their cases work through the labyrinth of federal immigration and legal systems isn't cheap. While most government programs are experiencing automatic across-the-board cuts under the federal sequester, this program got even more money this year. Congress gave $376 million to the Unaccompanied Alien Children program this year, more than double the $165 million in 2012. Nearly a decade ago, the program got just $54 million.

At one point last year, the federal government used military bases in Texas to temporarily house the overflow of undocumented and unaccompanied children in its care.

Advocates say the federal government worked around the clock last year to open several emergency shelters to move these children from holding facilities operated by U.S. Customs and Border Protection to the refugee office. The temporary shelters are now gone, replaced with an additional 1,300 beds in licensed homes and facilities, primarily in Texas.

The state no longer has over-capacity issues after some existing facilities were expanded and new ones were built, said Patrick Crimmins, a spokesman for the Texas Department of Family and Protective Services.

A decade ago, the United States would have routinely tried to deport the unaccompanied children caught at the border, arguing they were violating U.S. immigration laws. New laws put in place after 9/11 gave ORR the responsibility for caring and placing these children.

The Trafficking Victims Protection Reauthorization Act of 2008 provided more protections, requiring, for example, that the federal government interview unaccompanied children caught at the border to see whether they were victims of human trafficking, if they were eligible to seek asylum and whether it was safe for them to return to their home countries.