I have 3 dc. All with social communication difficulties to varying degrees.
My eldest has severe autism and learning difficulties. She is mostly tolerated wherever she goes. And that is really hard for her to accept. She knows the difference between people who accept that they need to accept her, and people who do actually accept her and are interested in her, as a person. She is 15 now, and still tries so hard, and it is just heartbreaking to see her amazing efforts at conversation and interaction being rebuffed, and not just by children/teens, but by adults too.
My middle child has Aspergers, and mostly manages to fit in successfully. Mostly. At great cost to her, it she would rather change herself than not fit in, sadly.
My youngest has high functioning autism, and he is struggling at the moment. He knows he is different, but doesn’t know how or why (he does know he is autistic, but is too young to really understand what it means), all he knows is that while he goes to great lengths to be inclusive of his friends’ wants and needs, they don’t do the same for him. So he will play what they want to play, but they won’t play what he wants to play. He will help them out if they don’t understand something, but they won’t explain things to him if he doesn’t understand. He would never dream of belittling anyone, or making them feel unwelcome, but they regularly laugh at him over things he doesn’t know, or exclude him because he ‘won’t get it’. There are times when I wonder just who has the social communication problems, tbh! I have had several meetings with ds’ teacher, as ds has had a really difficult year at school, and it isn’t just my (or his!) perception, it really has been happening as he tells me it has. And that is just heartbreaking. These are his friends, apparently.
OP, it is really hard, watching this happen in front of you. Seeing your children dismissed, as though they aren’t worth as much as another child. It gets harder as they get older/more aware. As I said earlier, dd1 knows when people are glossing over her, brushing past as though she is of no consequence. Tolerating her, but with no actual interest in her as a person. And she lest understand why she is not accepted in the same way as even her siblings (also disabled, but ever so much higher functioning).
I can remember dd2 being absolutely devastated when some of her year group laughed at dd1 because she was having an enthusiastic conversation about fire engines - dd1 was 12ish, dd2 was 10. Dd1 was talking to a teacher at dd2’s school, and was happy and excited that someone was actually taking the time to talk to her. And dd2’s peers laughed at dd1. Dd2 was upset, but also mystified - she asked me why it was ok for the boys to talk about Star Wars, or football, and she wouldn’t laugh at them just because she didn’t share the same interests, but they thought it ok to laugh at dd1 because she was having a conversation about something that didn’t interest them.
Tbh, dd1 is our canary in the coal mine, to an extent - if someone ‘gets’ her, and treats her as an actual human being, equal to them, then we know they must be a nice person. Sadly, all too often, people pay lip service to tolerating her - the smile that doesn’t reach their eyes, the obvious boredom with her choice of topic, the indecent haste with which they try to close the conversation and move on.
It isn’t just one person, once. It is most people, and all the time. Imagine a day where everyone you meet is desperately trying to not talk to you, not play with you, not sit/stand/walk next to you, not serve you in a shop, not engage with you in the same polite conversation other customers receive. And then imagine doing it all again tomorrow, and the next day, and the next, for the rest of your life. It is beyond lonely and heartbreaking.