I hope you are sure to say it in a hostile and angry manner as your post seems to convey. What a perfect way to display your faith!
Not at all, if my post came across that way, I certainly didn't intend it to.
Consider youself very lucky that your childrens' school still allows religious Carols. None of the public schools in my area do. All "Holiday" progams are now totally secular. And in the past when my son was in school, I never received the entire school program until the night of the program. It's possible that the parent who was compaining thought that an "inclusive" program would include some reference to the "reason for the season." Perhaps now the parents will ask to see the program details ahead of time.