I know you didn't ask for other options, but if families themselves are struggling financially, giving a small amount to donate to someone else might be a hardship on the family. I don't think I'd want to impose that now that so many are out of jobs.

Along the lines of TeacherPK6's idea, maybe your students could make various shaped small note cards (stars, snowmen, tree shapes) and write notes of appreciation for the school staff. They can hang them on the tree until the last day of school when they are distributed to whomever.

A friend of mine was big on recycling, re-using or re-purposing so she had her students create tree decorations out of previously used materials, or recylables. They actually were very creative in the projects they made.

Hmm, what about hanging handmade cards (made by the kids) that will later get sent to people (like deployed military, people in nursing homes, or something like that). The only thing is they would be late for Christmas so maybe they could be just general cards, but made in pretty colors?

I’m a bit confused. Are you putting things on the tree to give to them or are you asking them to put something on the tree to help others?

If their families are strapped financially, I would pass on altruism this year.

Socks. They are varied in style and color. Plus, socks are often the clothing item that needs replacing.

We will have a small tree in our room this year (100% Christian students). I want to have the students decorate it but I want it designed to help others. A lot of my students are struggling financially themselves. I was thinking a mitten tree or possibly a pet tree. Can you think of anything else that would possibly be free or low cost that would be in the theme of helping others? I knit a hat for each of my students and will have several extras that I donate to others.

Edited to add. Some of my students are struggling. Not all. It will be a low key, optional activity. They will be donated to a group outside of the school.