Jeffrey S. Passel, PhD, Senior Research Associate at the Pew Hispanic Center, in a Mar. 7, 2006 Pew Hispanic Center report titled "The Size and Characteristics of the Unauthorized Migrant Population in the U.S. Estimates Based on the March 2005 Current Population Survey," wrote:

“Unauthorized families with children come in many combinations of legal and illegal statuses, both among the parents and their offspring. Of the 14.6 million people in unauthorized families in the March 2005 estimates, there were approximately 4.9 million children. Of these, about 3.1 million children, or 64% of all the children in unauthorized families, were American citizens because they were born in the United States… Out of the total of 6.6 million unauthorized families, a significant share can be classified as being of ‘mixed status’ —in other words, families in which at least one parent is unauthorized and at least one child was born in the United States. There were 1.5 million unauthorized families in which all the children were born in the United States. These families represent about one-quarter of all unauthorized families and more than half of unauthorized families with children. Another 460,000 families, or 7% of unauthorized families, had both U.S. citizen children and children who were unauthorized. Taken together, these mixed status families represent about one-third of all unauthorized families and five out of six unauthorized families with children.”

Mar. 7, 2006