It's really not hard to find. .03 seconds with teh google.
http://www.politifact.com/truth-o-me...es-birthright/
According to a report by the Pew Hispanic Center, a think tank that has done extensive research on immigration policy, 3.8 million undo ented immigrants have at least one child who is a citizen. "Most children of unauthorized immigrants -- 73 percent in 2008 -- are U.S. citizens by birth," the center says. That's up from 63 percent in 2003.
These statistics suggest not only that the number is large, but is also growing.
To offer a concrete example, we found a 2006 article from the Dallas Morning News about Parkland Memorial Hospital in Dallas, a safety-net facility for poor residents. As many of 70 percent of the roughly 16,000 women giving birth annually at the hospital were immigrants who were in the U.S. illegally, according to one survey cited in the story.
http://pewhispanic.org/reports/report.php?ReportID=107
It's not an insignificant number nor an insignificant issue.