That can happen with homegrown children, too. Your very own heart-of-hearts darling child, for instance, who is diagnosed with severe autism at age 5 or gets slammed with paranoid schizophrenia in early adulthood. Mental/emotional illness is no fun.
Foster-care/orphanage kids present special challenges, which are bigger the longer the child was stuck in the foster-care system or orphanage. Our younger adopted son, Vanya, who came to us from an orphanage in the Russian Far East (Kamchatka), has had a real struggle.
At the same time, difficult as it's been, he has hugely encouraged our growth in faith, hope, and love. The challenged muscle strengthens. The challenged heart grows. God gives His grace, which is sufficient.
Much respect for your efforts.