EF, I have a particular faith and am doing my best to bring my children up to know about that faith and to follow its practices. It is not ok for a school to teach another practice to my children. I don't care if that practice is as seemingly innocuous as praying another version of the Our Father or as dreadful (imo) as insisting that my DDs cover their heads or pray separately from the boys.
If this is not what my family does or believes when it comes to religious practice, then I do not think a school has any right to make my small children either participate or feel excluded, any more than a school should impose vegetarianism on them and present it as the only way to live. I went along with the pledge of allegiance through gritted teeth in the US, but I would fight tooth and nail any attempt to have my children choose either to practice any other religion or stand out like sore thumbs because of refusal to.
When families are faced with that 'choice' a horrible message is sent to children of non coE faiths that the CoE is the mainstream and they are outsiders.
8 years old is a really arbitrary age to choose. There is really no age when anyone can be said to come to a definitive answer as to how they see things religion-wise. From the pov of many churches, the age when young people choose to become more committed (or less) can often be the age of Confirmation or Bar/Bat Mitzvah, but even the decision to go through that ceremony doesn't necessarily mean commitment that will last at the same level from then on will result.
As a parent who is bring up my children in a Catholic home, I would expect my children to be respectful of the religious practice of other families, not to expect to be fed whatever meal they fancied, cooked the way I cook it if eating with others, and generally to fit in, but I expect others to be respectful of my way of doing things in my home, and that expectation extends to schools respecting the fact that my children are being taught things that may be at odds with the CoE way of looking at things.
Until the DC is able to cook a non-veg meal for him or herself and clean up afterwards, then what the parent eats is what the child eats.