Thirty years of films, no continuity between them, and no correct order. Some starting points are better than others.
Start with Spirited Away
It is the most complete statement of what the studio does: a competent child in a world with rules nobody explains. If it does not work for you, the rest probably will not either.
Then by mood, not by date
For the pastoral register, My Neighbour Totoro and Kiki's Delivery Service. For the political Miyazaki, Princess Mononoke and Nausicaä. For the studio's other major director, Isao Takahata, Grave of the Fireflies — which is not a children's film in any sense and should not be shown to children as one.
Subtitles or dub
The English dubs are unusually good, and for the films aimed at young children they are the practical choice. The subtitled versions preserve performances that the dubs necessarily replace; for Spirited Away in particular, the original is worth the reading.