Kids can be cruel.
This is not quite the same as being read but it was a similar situation, on christmas day my father had invited my cousin over and his children, my cousin knows about me and is fine with it, uses the correct name and pronouns after I had a word with him but he haddn't told his children, it was somewhat awkward, I took his daughter aside and explained it and she understood perfectly, the boy I explained to while we were sitting at the dining room table talking and he just went beserk yelling "you're not a woman" again and again and again, I have a fairly thick skin but this completely tore me to pieces and i just shut down until my sister dived in and briskly took him away, he didn't talk to me again for the whole day.