I recommend "Ponyo". Because it's good :) I think this is possibly the Miyazaki movie for the youngest target audience of all his movies, but I don't know his early movies, only all the later ones that many people know.
Minimum age recommendations start at 0 (simply meaning no official limit, it's up to the parents) - depending on country - to around 5-7 years old for a minimum age for this movie.
IMDB: https://www.imdb.com/title/tt0876563/
IMDB parents guide: https://www.imdb.com/title/tt0876563/parentalguide
Minimum age recommendations start at 0 (simply meaning no official limit, it's up to the parents) - depending on country - to around 5-7 years old for a minimum age for this movie.
Wikipedia: https://en.wikipedia.org/wiki/Ponyo