I completely agree, Scarlett. How could anyone have done that to a child? The only royal fate that comes close (that I'm aware of) is that of Louis XVII, the son of Louis XVI and Marie Antoinette who was separated from his mother at the age of eight and spent months locked away in a dark room seeing no one. His treatment did improve after that but he died in prison at the age of only ten. You'd have thought they could have treated Ivan in a more humane way - especially as Empress Elizabeth was considered to be a warm hearted woman - but I suppose there was the constant fear of him being abducted and used as a tool to stage a coup if he were in any way visible to the public.
Yseult, the book "Five Empresses" by Ansimov has the most comprehensive discussion of the lives of Ivan's siblings that I've yet come across. Poor Catherine, the sibling who survived the longest and wrote the pitiful letter to Emperor Alexander was quite deaf and thus very dependant on her brothers and sisters. Apparently her hearing was damaged on the night her brother Ivan was deposed. In the scuffle in the royal appartments, Catherine was picked up from her crib and then accidentally dropped, damaging her hearing.
I also agree with you that Anna Leopoldovna was a very unlucky woman. Her own mother died shortly after Anna Ivanovna became Empress and she had no contact with her father, the Duke of Mecklenburg Schwerin. Anna Ivanovna doesn't seem to have had any great maternal feelings towards her niece and did little to prepare her to rule the country - hence the ease with which she and her son were overthrown.
The only picture I've ever seen of the internet of the adult Ivan is the one on Wikipedia that you mentioned, Scarlett. I did, years ago, see a drawing in a book that represented the meeting between Ivan and Peter the third. I don't know if it was just a drawing for the book or a copy of a painting - it looked very detailed so I suspect it was a painting, but I can't find a copy of it anywhere!!!
One rather touching aspect to this tragic story is that the children's father, Anton Ulrich of Brunswick, was offered the chance of returning to his native Germany (on the accession of Catherine the Great I think) but his children would have to stay in Russia in case they were ever needed for succession purposes. Anton Ulrich refused to leave his children and remained in Kholmogory with them for the rest of his life.