Because his parents made the wrong decision, so they ended up here illegally. If you don't agree with me, listen what Hillary was saying in that video.
No worries - I'm perfectly comfortable disagreeing with you AND with Hillary. Here's what I'm NOT comfortable with - rounding up some poor kid from Fresno who was brought here as a 5-year-old, grew up speaking English with American friends at her American elementary school, then went on to college or to work or whatever, and frog-marching her to the border of Mexico and saying, "hasta la vista, kid. Good luck!" If you're cool with that, I don't know what to say.
Incidentally, Hillary's not really addressing the kids already here, but rather the potential ramifications the law. You want to repeal DACA? I can see a case for it. But there has to be abetter option for those already here than, "later, dude. See ya."