I’m a trans mum. My kiddo was 11 when I transitioned. They called me dad for a while, because I told them they could use whatever feels comfortable for them.
However, their other mum (my ex, who I’m not on good terms with but is a genuine LGBTQ ally) pulled my kiddo aside and pointed out that calling me dad was probably making me uncomfortable.
So my kiddo had a chat with me about it. I ruled out “mum” because that’s what their other mum uses, and ultimately we just settled on my name.