I don't have children yet, but my wife and I will strongly encourage:
*Reading. Fiction, nonfiction, poetry... Subject or genre doesn't matter (within reason), as long as they love to read!
*Music-making. Singing, piano, other instruments if interested. Develops the mind, practice encourages discipline, heightens appreciation of musical genres.
*Imaginative free play. Building with Legos and other constructive toys, tabletop gaming, dolls/action figures, outdoor running-around roleplay, drawing, etc.
*1-2 seasonal sports. Soccer, baseball, basketball, swimming, etc. We're a little nervous about full-contact sports like football or hockey, but we'll cross that bridge when we get there.