Great question! Mine is Fiddler on the Roof. It may not be the first, but it’s the earliest I can recall.
Interesting question. I can’t really remember any pictures I saw in my childhood that stand out as memorable, at lest in terms of a quality film that I enjoy seeing again. I saw the early Fellini and Bergman films around 1960, and they were much more memorable. Also Satyajit Ray’s Trilogy of Apu, in 1961, which was awesome – I saw all three back to back played as a triple feature, in an art house in Saratoga CA. Also Last Year at Marienbad stood out for me. I was in my early 20s then.
Haven’t read the whole thread yet, but for me, has to be Gone With the Wind. I was in the third grade, and stayed up all night to read it in the bathroom, and then watched the film a few days later and was not disappointed. 
That is a true rarity. Although cultural mores have changed, I still think this is one of the best “early” films that I have seen. The compositions for each scene are incredible–I have often remarked that you could take any random still from GWTW and render it into a lovely painting. Do I need to provide examples?
The only other films I could compare that to were released around the same time…The Wizard of OZ (which I actually dislike for reasons other than artistry), the Hunchback of Notre Dame and The Good Earth.
My late grandmother loved to tell the story about how she begged to see that in the theater (she was about 5 or 6) and enjoyed it, but had nightmares afterwards, keeping her steel-worker papa up all night, till finally he gave her a bit of a paddling for being a pest. But, didn’t traumatize her enough to not enjoy watching it regularly with us grandkids once it came out on VHS in the 80s. 
My first memory of going to a movie with my Dad. In hindsight, I bet my mom and sister didn’t want to see a dumb comedy, but I liked being Just The Guys.
I still watch this and Rat Race (great homage/ripoff/remake).
I also learned about humor from the first scene. As the gangster dies, his foot knocks over a metal pail and the camera shows it bouncing down a hill. The cast stares in silence.
Me: “Psst, dad! They forgot to say he kicked the bucket!”
Dad: “It’s funnier this way.”
Me: “Huh?”
:memory jogs:
Pretty sure I saw Young Frankenstein when I was six. That will have to be my answer given that it’s impossible to pin down when I saw The Jungle Book.
TV – Roman Holiday, when I was twelve (or thereabouts).
Cinema – maybe For a Few Dollars More, when I was 13 or 14.