IMO, I don't think it's appropriate for a 4yo, but you be the judge.
From an online review:
"What starts out as a great idea for a fantasy movie quickly becomes an seemingly endless parade of heartless patricides, murders, forecasting the future with runes made from bone, killing animals and foretelling the future with their entrails, torture, murder, and reanimation with a voodoo doll, discussion of ritualistic cannibalism, animals devouring living people, and so many adult themes that it would take more time for me to list them than to watch the movie. How can you enjoy watching a father gleefully murdering his son while his other sons laugh, or women greedily planning to rip a young woman's heart out and eat it?"
"...every time another of the royal brothers murdered each other, a horribly disfigured, rotted, or axed-in-the-head ghost would appear in the line up of the funny guys who followed the still living brothers around. They made helpful comments that no one but us could hear, They popped up unexpectedly, watched the exciting parts of the story, including off-camera sexual activity (ok, only one of them wanted to see that). Then there was the demonic witch Lamia's constant changes back and forth from vixen to age-spotted, Shar Pei-style, wrinkled witch, with her hair falling out, cleavage going up and down, and rotting teeth."
"In my opinion, Stardust is not suitable for children, due to the disturbing scariness and brutality of some scenes. It might confuse or upset some younger viewers to see a beautiful actress (Michelle Pfeiffer) being so wicked and physically rotting. As there are no good, mature females in this film, the film distorts women's aging and maturing into an evil thing."