Although I think this kind of discrimination is disgusting, I can "get" the need to have a dr patient relationship that is more than just business and on a personal level, i.e. someone you are comfortable with. My doctor is straight/cis (I presume) but his nurse practitioner who I see is trans. And I actually like that I see her because I feel that she understands me and my needs as a trans woman more than a cis man or even a cis woman would. I feel that because of this I am very well taken care of.
But ultimately I think it should be up to the patient to choose and the doctor should seek to heal the sick, not impose their personal beliefs on the patient or patient's parents.