How to ask for "perks" in the middle of employment?

I'm an expat working in a private "VIP" school system. It costs about twice my yearly salary to attend here, but recently we've seen that they are starting to allow some employees (all natives, up til now) to have their kids attend for free.

I would like for my son, who is now pre-kindergarten age, to start attending. How can I go about asking my employer for this in a good way?

I do feel that I am underplayed for an expat, and they have recently increased my workload quite significantly. I worry that if I bring this up though, it might come across as a threat. This is the middle of the teaching year as well, so i'm thinking about waiting til the next year...but I really don't want to, it would make my life much easier.

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