Thanks for the info. I don't want to contradict a mom of a DS kid since clearly you know much more than I ever could on the subject! But, from what I have read, kids with DS have certain features that are detectable immediately by a doctor, at birth, like hand creases, etc. Of course I understand doing a blood test. Especially if a doctor doesn't want to come out and say, "Look, you child appears to have characteristics of DS." It's easier to say, "hey, we need to runs some tests here." Then, the test is done and may simply prove what the doctor knows and gives the parents certainty. In any event, by the age these kids are now, surely their pediatrician would know if there was an issue and they appear to have none of the features of classic DS.
I was interested to learn about mosaic DS. I'd never heard about that before! However, what I just read indicates that it is not Down Syndrome, but a disorder in which the child has some of the chromosomal abnormalities of DS but not all. I checked out this website that has tons of pictures of kids with the disorder.
http://www.trisomy16.org/html/mosaic16.html Looking at those pics, many people could have the disorder and in some cases it would be hard to tell by physical appearance exactly what's going on. Some have slight DS features but not all.
But the question was whether the Jolie-Pitt kids have DS, by which I take to mean, classic Down's Syndrome and IMO, they most certainly do not. I also don't think there's a chance they have any form of it, like Mosaic DS. They both look very normal to me, although the girl has a slightly bulbous forehead which is fairly typical in some kids.