He made a stupid joke. Let's not act like the left and pretend that jokes are out of bounds. (e.g.: "Hey, Russia! If you have Hillary's missing emails, it would be nice to give them to the press." "HE JUST ASKED A FOREIGN COUNTRY TO HACK HIS RIVAL! START AN FBI INVESTIGATION!")
Now, yes, he's completely stereotyping these children who are not only did nothing wrong, they did everything right and are STILL being slandered and libeled for it. Including by this jerk.
Because the left hates. It's their defining characteristic.