That is a family decision. I’m not going to be the one there taking care of the child. I can pontificate all I want to.
In general, just because the child has Down Syndrome, is usually not enough reason to prevent the birth. If the child has profound birth defects, that will make a stillborn birth very likely anyway, or endanger the mother, then perhaps so.
I wouldn’t dream of sitting in moral judgement of such parents, under those conditions.
Killing babies should be judged.