Thanks for giving Mum Chums a read.
I am transgender and a mum. I am the primary caregiver for my child. Talking with other trans parents, I have never heard of a class at a mainstream school with more than a couple of parents being trans. I get the impression that it is rare enough for any parent in a class cohort to be transgender.
It should also go without saying that if someone doesn't like a rule, they can do what they want.
However, as written, Mum Chums is a slice of life / kitchen sink drama about mainstream parenting spaces. The game is set to reflect this heteronormative (and to a far lesser extent homonormative) environment. Challenging aspects of parenting have been directly referenced rather than shied away from.