My memory is terrible so I don't really remember what I watched as a kid, but two children's films I rewatch every couple of months as an adult are The Cat Returns and Mary and the Witch's Flower. I could easily write an autistic wall of text about both, but I will try to restrain myself. Since someone already mentioned The Cat Returns I'll start with that one and write about Mary some other time.
There is a lot to like about the film, but if I had to focus on one thing, it would be the soundtrack. Yuji Nomi delivers a very whimsical, dream-like score very similar to his work with Nichijou. Nothing really draws attention to itself (except for Baron's theme), but it all blends seamlessly into the film from the very first note. I can't think of any other film that so perfectly sets the tone as quickly and effortlessly as The Cat Returns does.
The Cat returns is a very intelligent, competent children's film that handles its themes with great sensitivity. It's a story about personal responsibility, self-control, and living with purpose, but without losing one's personality and sense of whimsy. Not surprisingly, Disney was horrified by this and deliberately mistranslated key lines of dialogue in their localisation to turn the film into some dreary, solipsistic parable about 'being yourself'. The film is actually about time, hence the abundant time symbolism, which doesn't make sense if the film is about believing in yourself or something.
This makes recommending the film to English speakers awkward. Most seem to be unaware of the extent to which Disney fiddled with the text.
Fimm Unbelievably based taste.