About the only thing I might as you to consider adding is some background characters who have disabilities, and for whatever reason, money, pride, cursed, aren’t cured, maybe they don’t care if they can’t hear, it might be a blessing where they work.
I can see theo laying on the ground playing writing games with some kid and as S walks up, Kat touches kid’s head and they wave their hands about to each other before the kid waves to theo and runs off.
Nothing gets explained, maybe S is curious, but ignores it. And a few books later we might see theo waving his hands at the kid, but the kid lightly touches his hands like instructions.
Something S observed, but again, kinda dismisses.
At the school maybe have S almost get ran over because someone magiked the wheels on a wheelchair to go faster as a prank.
Though I can see her actually dealing with that problem, it’s gonna hurt someone.
Little tiny blink and you miss it nods, it’s a throw away, but only because none of the main cast has these issues.
Like the time where a group must have practiced for countless hours to be able to do a show telling a story with animation, sound, smells, and such.
Blink and you missed it, but this group was clearly active when not in camera.
They don’t need names, S doesn’t learn names of unimportant people, they don’t even need more than a few paragraphs, but they are there.
Your LGBQT, blind, on spectrum people, front and center, glasses wearing also there, ethnic differences is such a non issue for the most part, freaking awesome. It’s more if your poor than genetics 
You are already so inclusive, and you have throw aways of beings in the background who have clear [to me] history, hopes, aspersions. Personally I don’t care if they have names, but they are there.
And all I am really asking for is you never stop with your throw away moments. S is super observant, stuff catches her eye, instead of Theo and the signing child, it could just as well happen at the college or the meeting. I just like the idea that Theo doesn’t even flinch at playing with someone who doesn’t speak and instead plays in a way that they can participate. Also, Kat would prob love it because it gets Theo to work on his handwriting and all the other skills that comes from those games. The idea of Theo eventually deciding to learn to sign is sweet.
The child doesn’t have to be deaf, though it would be assumed until someone tried to talk to the person without being able to see their face. Cause lip reading is a thing.
As someone who was non verbal as a kid, I almost never spoke unless forced to, or trusted who I was with to not make fun of me. I still wish my family had let me learn to sign.
Can anybody else think of throw away moments to be more inclusive?