There's no point celebrating Cinco de Mayo anyway. It has nothing to do with US history. It's like celebrating the Battle of Hastings, or the Punic Wars, or some other country's old-time military victory. Whoop de doo. There's plenty of other US military victories that we don't celebrate, either. Can't have holidays all the time. And Cinco de Mayo isn't even heavily celebrated in Mexico (according to wikipedia).
I think the school was wrong to send the kids home. Nothing wrong with celebrating your heritage - either as a Latino or as a US citizen. Would they have gotten thrown out if they wore german or english flags? Or whatever their ancestral ethnicity is.
We do not bow to kings and queens and we do not bow down to any other country's flag. That's what the founding fathers were about.
But we have also given our government's word, for what it's worth, to respect the traditions of the conquered peoples of the Southwest.
This includes refraining from heaping scorn on their holidays. It also includes educating our citizens in those traditions, so that we may give them due respect.
The irony of it all is that Cinco de Mayo, as Wyatt so eloquently put it, is a [censored] holiday. It's of no importance in Mexico and mainly a pretext for drunkenness in the US. It was certainly not worth this squabble.