Thousands of unaccompanied children continue to cross the southern border into the United States, Homeland Security Secretary Jeh Johnson told Congress on Thursday.

The number of kids entering the country is down about 40 percent from a year ago, though, Johnson told the House Appropriations Subcommittee on Homeland Security.

"I hope it stays that way, but we have to be prepared in the event it doesn't," he said, reported CNS News.

Johnson said that last year, the total number of unaccompanied children apprehended was about 68,000, but this year, he expects the total to be between 27,000 and 40,000.

January 2015, with 2,121 children apprehended, was "actually the lowest monthly number we've had in quite a while," Johnson said.

In February, 2,395 children were picked up at the border, whereas in February 2014, the number was more than double that, at 4,845, Johnson noted.

He estimated that the numbers for March would be "around the 2,600 or 2,700 level," well below the 7,176 children who crossed in March 2014.

As the weather gets warmer, the number of unaccompanied children crossing the border is expected to increase, Johnson said. "If they're going to creep up, they're going to creep up right now."

"The high for the unaccompanied kids was June 2014, that was 10,620," Johnson told the subcommittee.

Since the start of fiscal year 2015 in October, the Border Patrol reported apprehending 12,509 illegal immigrants under the age of 18, constituting "the second-biggest surge in history after last year's unprecedented movement of unaccompanied youths across the nation's southern border," The Washington Examiner reported last week.

Immigration and Customers Enforcement documents revealed that only one of every six children were actually being returned to their home countries, noted Newsmax.

As part of its budget, the Senate on Thursday approved non-binding language which asks that the law be changed to decrease the time it takes to deport illegal Central American children back to their home countries.

Sen. John McCain, R-Ariz., who pushed for the change, said it is needed so that the surge of Central American children expected to cross the border in the coming months are aware that they will be sent back to their home countries rather than released into the U.S., as they were last year, according to The Washington Times.

Current law allows the government to quickly send unaccompanied children back to Mexico, but children who come from Central American countries like Guatemala, Honduras and El Salvador must be processed and released to social workers inside the U.S., the Times reported.