A new analysis of U.S. Census data by the Pew Hispanic Center reports that while undocumented immigrants make up approximately four percent of the adult population in the U.S., their children represent eight percent of the newborn population and seven percent of the child population (younger than age 18). Factors explaining the difference include the relative young age of immigrants and their greater likelihood of having large families.

The report comes amid growing calls by conservative lawmakers in Washington to consider repeal of the 14th Amendment to the U.S. Constitution, which endows citizenship to anyone born in the U.S. The debate began in early August following comments made by Senator Lindsay Graham, a Republican from South Carolina, who told Fox News that the amendment no longer serves its original purpose and should be re-examined. He and other politicians argue that fewer people would cross the border if they no longer had the incentive of giving birth to U.S. citizens.

The report also arrives as 224 U.S. National Guard troops prepare to deploy along California’s southern border on September 1. The troops will assist with counter-narcotics, anti-illegal immigration and other border security operations.