Most kids wear very routine stuff anyway, cartoon characters and super heroes.  The little kids costumes are pretty predictable.  
Are high schoolers wearing crazy offensive stuff? As kids get older, they usually stop dressing up anyway.
I drop my kids off at school every Halloween and I haven't seen anything controversial. Maybe a couple boys with light sabres that are asked to stop swinging around.  That's pretty much it.

Tempest in a teapot.