The job of reuniting migrant children with their parents, is proving easier said than done for US authorities.

Thousands of children, toddlers and babies have been separated from their parents and detained on the US-Mexican border.

Donald Trump has signed an executive order to reduce the controversial practice.

But US correspondent Richard Arnold told Mike Hosking the government has no records for most of those currently detained.

"The government now says it is working to provide that kind of data base but there are still hundreds of kids who are being held apart from their parents."

LISTEN ABOVE AS RICHARD ARNOLD SPEAKS WITH MIKE HOSKING