They are just kids, being stupid.
And building a wall to keep out illegal immigrants is not racist, no matter how much you wish it to be. A wire fence and wall already exists for good reason.
Can explain why it is not racist then?
In the campaigns, those words awokened the "it's the mexicans' fault" belief in the minds of many.
They felt the relief that someone has promised them that mexicans won't be able to enter the country anymore and all the mexicans around them will now be deported. All the frustration vented into a group of people.
They want satisfaction while ignoring the the well beings of this other group of people which live a harder live to begin with.
The selfishness, the want for this group of people to disappear, the hate is what makes it racist.
I don't get the "they are just kids being stupid" excuse. It implies that it is okay for kids to practice toxic behavior because they are kids.
They don't need harsh punishment and expulsions.
What they need is to be taught proper values and proper education on these matters.