The American Immigration Council reports:
“Since fiscal year 2010, over a quarter million parents of minors who are American citizens have been deported. These numbers…. likely do not reflect all of families that have been torn apart. ICE’s reports only include those who volunteer information about their children; many may not disclose this fact, fearing for the safety and future of their children.”
An estimated six million U.S. citizen children live with at least one family member who is undocumented. This is 8% of all children in the U.S. Using Pew Research figures, this means that one quarter of the current second generation immigrant population under 18 (27 million) has at least one unauthorized parent.
(For second generation figures see appendix 1 here)