Best if the old movie is made before 1990
It’s a Wonderful Life, every time
Several plot points in that film are absolutely horrifying like the shopkeeper deafening him as a child
He was deafened by an ear infection after diving into a frozen pond to save his brother from drowning. Later he prevented Mr. Gower from accidentally poisoning a child when Gower was distracted by grief. I do believe Gower hit him during that sequence though, if that’s what you’re referring to. And yeah that last part is rough but sometimes life and history are unpleasant.
Grave of the Fireflies is a good one and has been mentioned a few times already.
Fox and the Hound has several tear jerker moments, though most memorable for me is when Todd is returned to the forest.
Land Before Time was my first parent death in a film that I can remember. And unlike Bambi, this movie shows more of the consequences of losing a mother at that young of an age.
Star Trek II: Wrath of Khan always makes me cry. The death of Spock, the exchange between him and Kirk, it always kills me.