All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
There is no doubt that what this school helper did does not constitute Kufr or Shirk at all. Even if he did photocopy those work sheets, this act in and of itself does not constitute Kufr or Shirk. At worst, he neglected to clarify the impressibility of such an act and forbid the teacher from doing it.
If these papers were about celebrating Christmas or inviting to that, then, the Fatwa of the Permanent Committee for Islamic Research and Fatwa reads: “It is prohibited for Muslims to support unlawful festivals by any means, whether by supplying food or drinks, selling, buying, manufacturing, gift-giving, corresponding, advertising and so on, because all this falls under cooperating in sin and transgression, and disobeying Allaah and His Messenger. Allaah, The Exalted, says (what means): {And cooperate in righteousness and piety, but do not cooperate in sin and aggression. And fear Allaah; indeed, Allaah is severe in penalty.} [Quran 5:2]”
However, supporting the celebration of non-Muslim religious festivals per se does not constitute Kufr or Shirk. For more benefit, please refer to Fataawa 88780 and 133510.
Allaah Knows best.