Maggie when I was a child I was always told that children who were adopted were "special" because they had been chosen by their parents whereas such as I was just gotten 
Yes Susie, you were common or garden.

When we adopted in the 1980s it was the practice to tell a child that they chose their parents as opposed to the other way round. It was thought that telling a child he/she was chosen put too much pressure on them and cause them to feel they had to be 'grateful' and try to live up to an impossible ideal.
In the 1960s and 70s children usually didn't know they were adopted until like Sheila and Jeremy they were told, out of the blue, it was the way adoptees were told to do it and must have been very traumatic to the children and the parents involved, just an awful way to treat a child and awful thing for parents who loved their child to have to do.
I don't know what is suggested these days. My children always knew they were loved because they were and children know if they are, I simply cannot understand how anyone can adopt a child and not love that child with a passion, makes no sense and is very cruel. imo