I do want to preface that I've known several people in my generation who were adopted, are loved and are just fine.
I did have a close childhood friend, we were pals into early 30's friendship where I knew her family well. Her parents adopted boy when he was around 3-4 yrs. old At times, through the years I would hear of the problems with her brother. Total contrast to rest of his 3 sisters. He got into crime, several times in jail, drugs, etc. Didn't finish high school. Left home. He did eventually clean up and married a nice woman. I met her.
Then several years later, I heard he died. He was only in his late 20's. The reason for his death was never really given. Like a dark cloud hanging over the family.
For a totally different family, I've always wondered of what happened to this huge family, that we knew where a Caucasian couple (professors) had 2 natural children and adopted 5 other children..wide range of backgrounds, several black, 2 native Indian, etc. This was highly atypical in small southern Ontario city when I was growing up to have a large family of primarily adopted children. At the time, it was source of curiosity because it was predominantly white city at the time.
Even as children we knew some of the adopted children had some learning (meaning disruptive) challenges in the classroom since some were in classes with some of my siblings.