Here's a possibility to consider: Dear parents, Every two weeks (or sometimes more often), we take time to get our "paperwork" in order. But I do have a question -- what do you mean by paperwork? For kindergarten, I'm wondering if this is a project you do with them, in which case it would be "working with paper", but if it's actually getting the "paperwork" in order, this expression would mean that students are making sure their homework is done, signed off on by parents -- paperwork is generally a term that is used for adults with a lot of paper (that is, bills, letters, documents) they need to sort out. For kindergarten, I'm curious what a paperwork class means in your situation.

You could say "Once every week or two, we hold..." or "once a fortnight" if it is every two weeks. If the paperwork class is sometimes one week and sometimes two weeks apart, then you should say "once every week or two". "A class is to be held" is another way to say it, but "we hold a class" is not particularly informal.

Here's a suggestion: Every week or so we have a paperwork class in our kindergarten. (What is a paperwork class?)