even though Christmas is seen as a pagan festival, it wouldn't be celebrated if Christians hadn't come up with the story of Christmas.
So what, @BlueSlipperSocks? It doesn't mean no-one is allowed to celebrate Christmas unless they are fully paid-up churchgoing christians. Hallowe'en wouldn't be celebrated unless someone had come up with all those notions of witches, wizards, ghosts, imps, goblins etc, it doesn't mean that anyone says that only full-blown believers in witchcraft and ghosts are allowed to have a Hallowe'en party.
If OP wants to pick and choose which elements of Christianity her children are allowed to take part in then maybe home education is a better option for her children.
No, a better option would be for the school to obey the law.
It would save unnecessary disruption to the class as teacher tries to figure out whether these precious children should be present for religious teachings, or not. And then have to find somewhere to put them whilst the rest of the class is taught as per curriculum.
As has been pointed out to you previously but you keep ignoring, OP is happy for her children to be present for RE lessons, so the point doesn't arise. As for finding somewhere to put them during assemblies, the school has had no problem with this for some years, and has no problem with it in relation to OP's second child, so why would it suddenly be a problem now?
And yet all Primary schools put in a little play at Christmas entitled "The Nativity", which whether you like it or not is a Christian story about the birth of Jesus.
No, they don't.
Your poor children having to be segregated from their peer group and fun lessons for no reason at all - except your bigoted views!
As you well know, they aren't segregated from "fun lessons": they are removed from one assembly once a month run by a church minister. There is no evidence that these are "fun". And describing OP's views as bigoted really isn't showing any sort of christian tolerance on your part.