First of all : I've never seen a 5 or 6 six year old nun. But I see 5 or 6 year old little children with a hijab. Yes little children, because they are female.
What this means is by far more than just cultural, you need to read the koran for that (I did). If a grown woman decide all for herself to do it, I'm fine with it, but the reality often look totally different.
To be honest, I'm not sure, what Maxis was thinking. I wasn't expecting such a step from an american company. On the other side : sure, everybody should be able to play the game the way they want. And exactly here is the problem :
Sims 4 the game where the game decide what my sims wear and I don't want to see a single sim (children or adult) wearing a hijab. So yes, until the game stops to change my decision for the clothing or I get an option to disable the hijab, I have a huge problem.