The decision comes with Homeland Security officials increasingly concerned about child trafficking as a growing number of Central American families cross the border, straining resources to breaking point.

Border authorities also recently started to increase the biometric data they take from children 13 and younger, including fingerprints, despite privacy concerns and government policy restricting what can be collected.

The Department of Homeland Security wouldn't say on Wednesday where the DNA pilot would begin but indicated it would be as early as next week and be very limited.

The testing will happen once officials with US Customs and Border Protection, which manages border enforcement, refer instances of fraud to ICE, which usually manages interior enforcement.

But teams from ICE's Homeland Security Investigations were recently deployed to the southern border to help investigate human smuggling efforts.

The rapid DNA test will take about two hours and be obtained via a cheek swab from both adult and child. The parent is to swab the child, officials said.

The testing will be destroyed and won't be used as evidence in any criminal case.

Generally, US officials determine a family unit to be a parent with a child.

Fraud would occur if a person is claiming to be a parent when he or she is another type of relative, or if there was no relationship at all.

ICE officials say they have identified 101 possible instances of fraudulent families since April 18 and determined one-third were fraudulent.

Since the beginning of the budget year, they say they have uncovered more than 1000 cases and referred 45 cases for prosecution.

The fraud could also include the use of false birth certificates or documents and adults accused of fraud aren't necessarily prosecuted for it; some are prosecuted for illegal entry or other crimes.

Homeland Security officials have also warned of "child recycling," cases where they say children allowed into the US were smuggled back into Central America to be paired up again with other adults in fake families.

But the department hasn't identified anyone arrested in such a scheme or released data on how many such schemes have been uncovered.

Advocates say they're worried that in the name of stopping fraud, agents might take personal information from children that could be used against them later.

DHS officials say the program will be done with existing funds.

Earlier on Wednesday, the White House said it would need an additional $US4.5 billion ($A6.4 billion) in humanitarian aid for the border.

Australian Associated Press