Have you considered that children are entitled to learn about everything on offer if they are to live as adults in a world where understanding one another is the key to living in society? We always hope our children will choose for themselves what faith they want to follow, but how can they do that if they are not allowed to learn about other faiths?
@llizzie, why ask this when OP has made it clear more than once that she is happy for her children to go to RE lessons?
How do your children feel about being separated from their friends?
@susantrubey, OP has said they are fine with this. What's the big deal about being with your friends in an assembly once a term anyway?
I just wondered what do you do when it is Easter, and Particularly Christmas? Do you tell your Children they cannot celebrate these occasions?
This point has already been made and answered several times, @Lizziejane63. It's perfectly possible to celebrate Christmas and Easter without being Christian, given that both events are rooted in pagan/Roman origins.
If it's so great to learn of other cultures by attending church assemblies, the school should be putting on assemblies run by ministers of all religions, not just the Christian one. And, yet again, OP's children go to RE lessons, therefore they have plenty of opportunities to learn about the religious practices of all cultures.