What would your reaction be to something like this?

I recently met a young woman who has a son who is mildly autistic and who has a speech impediment. You know how we sometimes repeat our children’s comments or questions back to them? Like, the kid says, “I want a cookie!”
And you say, “You want a cookie!? What are you going to do with that cookie?!”
You kind of start a dialogue that way.
Well, this child said, “I aut a gwas ov juoth!”
And Mom said, “You aut a gwas ov juoth?!”
I was completely FLOORED.
I don’t understand.
Why would someone do that instead of repeating it back clearly, especially to a child with a speech impediment?