I agree, such a sad film with Ann Margaret as the mother. Another movie, set in the same sort of era is After the promise, starring Mark Harmon. His wife also dies, and all his boys get taken away, and put into institutions, he then promises his dead wife he'll get them all back. The final scene where he eventually is reunited with his eldest son Richard, is so emotional and gets me everytime.
Marley and me is also very sad, our 2 jacks are 15 and nearly 13 now, and as a great animal lover, it really choked me up. Also Alpha Dogs, the movie debut of Justin Timberlake, is absolutely heart breaking, and is one film i could never bear to watch again.
One flew over the cuckoo's nest, starring Jack Nicholson is also incredibly sad.
As is, Boys dont cry, starring Hilary Swank.