JUDY WOODRUFF:

Bush campaign aides call the practice birth tourism, with foreigners arriving legally just in time to have a child.

Numbers are hard to come by. The nonpartisan Migration Policy Institute estimates some 230,000 children are born in the U.S. each year with at least one parent here illegally, while the Center for Immigration Studies, which favors stricter rules, estimates 36,000 births a year by women who come to the U.S. to have a baby, then leave to go back home. Others say that number is smaller.

Meanwhile, the issue has now become part of the broader immigration debate.

To help explain the background on this, I'm joined by Doris Meissner, senior fellow at the Migration Policy Institute and a former top official at the Immigration and Naturalization Service under President Reagan and its commissioner under President Clinton. And, Susan Berfield, she's a reporter with Bloomberg Businessweek.

We welcome you both to the program.

I think it helps to have everybody first understand that we appear to be talking about two different practices here, first children born in the U.S. to parents, one of whom — at least one of whom is here illegally.

Doris Meissner, what are the typical circumstances there?