Wow. Defensive much?Sure... as long as your 4 year old is quiet.
Don't like kids ruining your movie, then don't go to a matinee or the early show. And age is not an indicator of being quiet anyway, some so-called adults can ruin a film experience just as easily, or actually worse. If it really bothers you that much and you don't want to take the chance, you could always wait for the DVD and watch it by yourself.
People shouldn't talk during movies. Period. No matter what age they are. If they can't resist talking, then they are the ones who should stay home and watch by themselves.
As for the OP's question... it can't really be answered unless you know the kid. Some four-year-olds understand fast-paced complicated stories; some don't. Some are easily scared by vivid images and loud noises; some aren't. There's nothing in the movie that I'd consider downright out-of-bounds for small kids (it's not Watchmen), but it's entirely possible that she simply might not Get It.