This is definitely not the kind of thing where the police should be involved. The school should not tolerate immature pranks intended to offend minority students, but it's extreme to call it a "hate crime".
If the kids are caught, they should get the usual school-sanctioned punishment (a few days vacation
)... It's up to the parents to punish them the rest of the way. Sad part is that the parents might not frown upon it... but it's not like getting the police involved is going to help anything.