Either Bambi or Bedknobs and Broomsticks. I can't remember which was first, but I do remember that B&B seemed magical to me, the way it was a mixture of real people with animated backgrounds and magical situations. Perhaps this is why I much later was so impressed by magic realism such as (principally) The Master and Margarita. Disney as preparation for Bulgakov!!!
FWIW, I think the Disney films made by Disney, as opposed to the later stuff (yes, I know B&B was later) is a lot darker than is popularly supposed. Bambi didn't leave much impression on me, though.