I just want to make a point about the use of "disabled child" or "autistic boy".
In the phrases "a child with autism", "a child with DS", you are embedding the information about the disability after the subject. Some believe this is putting the child first, but for some people writing/saying a sentence in this way is actually a good deal less "natural" (and I mean this in terms of how they say sentences usually, not how they talk about disability) than putting the adjective before the subject. A great many people will never say "the girl with the black hair was playing on the swing", or "the boy with the blonde hair was kissing the girl with the red hair", as this type of sentence structure is unnatural for them and takes slightly longer to process.
This doesn't mean that if they choose to "head" the sentence with the adjective that they are foregrounding this information because they think it's more relevant to who that person is, but rather because it is more relevant to what they want to highlight in the context of that discussion e.g. If I say "the red-headed girl gave it to me", I am not viewing her as a red-head first and a girl second, I am saying that out of all the girls that I could be talking about in the crowd, I am talking about this one. I highlight the information that makes it easiest for you to process who I am talking about.
So there's a subtlety there. If the information is given redundantly e.g. I say "Johnny the Downs Syndrome boy" even though there's only one child who has DS in the class, that's likely to say something about what the person thinks e.g. but arguably, that's the case no matter how you present that information. For example, if someone says, "my sister is going on a date tonight" vs "my sister is going on a date tonight with a black man" or "my sister is going on a date tonight with a man who is black" how that information is given about the colour of the man's skin is irrelevant. The point is why does that person think that information is relevant? And there are different possible interpretations based on what the person giving the information thinks about black people.... it could be that the speaker's sister is black herself, and doesn't agree with interracial dating, and that she is happy that her sister is dating someone of her own race. Or it could be the more obvious form of racism. Context is everything.
If I read "Curious George" to my toddler, I always simplify "the man with the yellow hat" by chunking the sentence to "The man is driving", as I know that for a 2 year old who is just learning to talk and listen to a bedtime story, "The man with the yellow hat is driving" is just too much to process. I am not denying the importance of the yellow-hat to the man, nor am I refusing to see him as he truly is because I omit this information. In the same way, it can be a bit of a leap to suggest that because someone says "the autistic boy", "the Down's boy" in a conversation where the fact of the disability is of high relevance to the discussion that they are denying the personhood of people with disabilities. Remember, many in the Deaf community prefer to be called Deaf rather than "a person with hearing impairment". I also know several adults with autism who see their autism as central to who they are and describe themselves as "an autistic woman" or "an autistic man". We all interpret these things differently, and that's fine.. but it is best to assume the principle that generally average people who are not aware of the politics do not intend to insult when they use language in this way.