What you've linked to is a discussion by non-JWs about how much they can involve a JW kid with Christmas festivities/celebrations. That's entirely different. The JW kid will not partake in any Christmas celebrations or tradition.A quick Google presents loads of people with the view that chap has shared.
Here is one for instance: https://forums.atozteacherstuff.com...itness-and-how-to-handle-the-holidays.153892/
The question was whether to cancel Christmas celebrations for pre-school because one girls Mum was offended.
Edit: One person has legit suggested they can't watch the Polar Express, lol.
That's entirely expected. They don't celebrate. This is known.
(But what that means/should mean/always used to mean is that the JW kid does something else whilst the others get on with it.)
What isn't expected (or correct, imho) is restricting the teaching of the RE curriculum based on a JW child being present, who has opted in to that module.
e: Incidentally I find the teaching of RE in schools to be completely undesirable. Religion should stay the hell out of school life.