The problem with religious clothing is that the more people who wear it, the more pressure can be put on children to wear it or stand out/be condemned. It gets worse when the clothing is gender-specific.

It also puts children in a situation where their religious background can be seen from afar, making them Christian/Muslim/Jew etc. first and citizen second, when in a secularised country it should always be the other way round.

It is twice as bad when teachers wear religious clothing, because how can you not wear it if your teacher is wearing it. And when children wear religious clothing and have to defend wearing it, they get into a situation where they may have to defend it and wear it and even be part of peer pressure because there is no way out, you are either pushed from one side or the other and many choose to then rather push themselves.

Religious freedom is a double-edged sword: Freedom to live your religion, but also the freedom to live without religion, and especially children who are brought up in a religious family need the school as a place where religion isn't a thing, so that they have a place to even think about what it feels like to live without it. Religion needs to be a personal choice and only if you have a place to check what it means to be without it you can choose.

If your religion can not give children a place to be without it so they can then freely choose, there is something severely wrong with that religion. Unfortunately I have yet to find a religion that does allow it.