There are many people in our society that are able to live in a way that they choose so just because you may not agree does not mean to say that a 9 year old cannot hear about it in an age appropriate way.
The appropriate is the key part here.
'People can dress any way they like within the bounds of appropriacy and respect for the situation/others' (has to be added because bloody hell have we seen open mindedness pushed to the stupid point and beyond by exhibitionists, butt monkey being one of the well known examples. Currently presenting man teacher with boobs to the knees and clearly visible nipples another.) 'There is no right way to be a boy or a girl, a boy can dress any way he wants and wear and do whatever he likes, and still be a boy, and it's good to be yourself.'
Fine. Great. Let's wreck those stereotypes. Everyone's body is perfect as it is, and they are perfect as they are.
'Some people have a condition where they are distressed and unable to accept the sex of the body they have, and prefer to dress and have a name or even grown ups change their bodies to look more like the sex they want to be, and it's kind not to point out that this isn't a real change.'
Also fine. With clear limits on how far my child is expected to be kind, and that it is not ok to make other people uncomfortable or remove their privacy or expect other people to give up their normal boundaries rather than jar this preference. There are times and places in which stating reality is necessary if someone is forcing you into it, and it is not wrong to do so.
'Everyone can pick their sex, you can change sex, you can be the opposite sex if you want to, it's all harmless and can be undone at any time including surgery and drugs, sex is a spectrum, homosexuality means you should go by what the person tells you and not what your eyes and body and sexual desire tells you, don't call yourself a girl, it's bad and only nasty people do that, some kinds of people are more important than others and if you're an important kind of person you get to tell other people what language to use and how to treat you and if you're not that important kind of person your job is to shut up and look after the more important people, your parents are old and wrong and stupid and you should break contact with them and go only with online adults who will love and support you much better than the people who raised you ever could, anyone who says no to you says that their reality matters too is a nazi' -
absolutely bloody not fine, and to pretend this isn't part and parcel of it, and what kids are taking away, is naive now to the point of being ridiculous. Adult discomfort with cognitive dissonance is not an excuse to take advantage of children's trust and lack of experience of the world, and to enable a political movement with a lot of unaddressed problems to control 'messaging'.