Washington(CNN) The US Border Patrol has begun fingerprinting some migrant children 14 and younger because of increased concern about fraud and the trafficking of children, a senior agency official said.

The agency issued guidance to the field several weeks ago to allow for the fingerprinting of children, which is being done on a case-by-case basis in the Rio Grande Valley region of Texas when trafficking is suspected, said the official.

Immigration authorities have raised concerns that children may be exploited and trafficked as the number of family members illegally crossing the southern border has reached record numbers and continues to rise.

"Right now, we are still faced with overwhelming numbers. Every tool that we can get is going to be helpful for us," said the senior official, regarding the collection of the biometric fingerprint data. "Ultimately, it's the changes in law" that will have a lasting impact, "but this will help us counter the fraud."

More migrants were apprehended along the southern border in March than in any month in more than a decade, according to Customs and Border Protection data. In the Rio Grande Valley, Border Patrol apprehensions so far this fiscal year have already surpassed apprehensions for all of fiscal year 2018, the agency announced this week.

The fingerprinting of young children, which is a shift from prior policy, is taking place in at least two regions along the southern border -- the Rio Grande Valley and Yuma sectors, according to officials.

Prior to the new guidance, Border Patrol occasionally took photos of children, and collected additional information, but did not fingerprint migrants under 14, said the official.

From a technical perspective, the reason Customs and Border Protection previously did not fingerprint children until they turned 14 is "because your fingerprint doesn't solidify until that time," said a former DHS official, who worked on immigration policy and biometrics.

Fingerprint algorithms rely on features that are consistent only after 14 years of age, said the former official.

It's unclear what privacy or legal concerns this shift in policy will raise.

The Yuma Border Patrol region, which includes part of the US-Mexico border in Arizona and California, began running a test program several months ago to fingerprint certain juveniles in an effort to combat the issue of fraudulent families encountered at the border, according to agent Jose J. Garibay III, in the Yuma Sector public affairs office.

The program, which was conceived at the local level and implemented with guidance from headquarters, began because agents in the region were identifying a "large amount" of family fraud, said Garibay.

According to Garibay, the Yuma sector has discovered 600 fraudulent families since the start of the fiscal year, which could include a child who is being trafficked or a child with non-immediate family members, such as a cousin.

During the same time period, more than 24,000 family members were arrested for illegally crossing the border in the region, according to CBP data.