I wouldn't go out of my way to visit my half-brother, if I discovered he was in an institution. We have hardly any relationship, we've met a few times. I don't feel I have any responsibility for him.
One of my oldest friends has a disabled child who is unlikely to ever live independently. We see them regularly, and when she goes into whatever form of supported living, at whatever age, I will certainly visit and stay in touch.
So no, I don't judge QE2 for not springing into action for two cousins that were first referred to as dead, but then turned out to be alive and apparently receiving adequate care.
The 200 members of extended family mentioned above were people she had a relationship with, the cousins she knew growing up (and their children and grandchildren, who she had known all their lives) plus her own children and grandchildren.
I would hope that in this day and age children with disabilities would grow up as full members of a family, and have those on-going relationships. Sadly, in the past, often they were removed from families and institutionalised.