First, who names a son “Coy”? That’s odd right there.
Second, I think there’s a good chance that Coy sees that Mommy is the one who makes all the decisions in the family, so he wants to be like her, instead of his father, who has become wussified to the nth degree.
I don’t think that at 18 months, Coy was deciding he was a girl, his mommy was deciding it.