It is not their 'statutory duty' to interfere in everything and dictate what's what.
I'm pleasantly surprised that the parents kicked off about it. I would have too, for several reasons.
1). It's my personal belief that people should be allowed to explore religions when they're old enough to have an understanding, and not before.
2). No religious representatives that I've ever encountered present their beliefs as anything other than fact. So youngsters being forced to 'explore' a variety of religions, are being bombarded with a lot of completely contradicting (so called) 'facts'. And there's a whole lot of fear & implied requirement for guilt thrown into the mix with many religions who preach that it's sinful to not believe/follow whatever version's being spotlighted, with the threat of eternal torment for them.
3). Schools should be focusing on literacy, numeracy, science etc, etc, etc, and some imparting of moral decency. They don't seem to have mastered that yet in a great many cases. There's no necessity to include any religious indoctrination at all.
4). As religion is about personal choice, it's none of the school's business.
5). It's an absolute bloody cheek for them to use any form of threats - particularly the labeling of a 4 to 6 year old as racist. It shows their pig ignorance anyway, because religion is a thing that in itself is distinct from race.
6). Where do they get off stating only a GP's note will prove a credible reason for absence! Cheeky bastards!
I could go on & on. But I've bored myself now.