It seems to have been done to illustrate the effect Trump is having on kids. The point over whether the parents should be allowing their kids to do this sort of thing is debatable and you are making good points about it, but it's at least controversial enough to get the message across. There are other links in this thread that talk about stuff that is really happening in schools, like hispanic kids bringing their social security cards to school out of fear that they may be deported. Many kids are terrified of being forced to leave.