I don't know that it's millions, but I take your point. There are certainly a lot of them being born in Texas (and every other border state) today.
One thing that may give you a bit of comfort, is the fact that on average, roughly 1,350 Americans move to Texas every day of the year. That's a little under half a million a year, and lots of them are having babies too.
I moved to Texas from California eight years ago, and brought four Rush babies with me :-)
I also had four, so we both are doing our part :)