Parents use appropriate caution and it can be a learning opportunity
We watched this with our four-year-old son on pay-per-view, because my husband wanted to see it. Our son has been taking tae kwon do since he was two (for the discipline, exercise, self-confidence, male role model, etc.), and we thought he might like to see what older kids learn from their martial arts masters and how they compete. The class has been good for him and we wanted to encourage him to continue with the sport.
Our son did like the martial arts part of the movie, and the main characters (Dre, his mom, and Mr. Han). The romance was totally over his head, so it was not a problem - it wasn't so obvious as to make him ask questions. He is also not too aware of racial or cultural conflict yet, so that didn't come up except to talk a little bit about why the bullies picked on Dre.
The language used between the bullies and Dre, and the bullies' behavior in general, did bother us, especially because the length of the movie made it hard for younger ones to grasp that in the end, the bullies had consequences both from their bad choices and from following a bad role model (their kung fu master). But we were prepared for that because of the original movie, so we did talk to him about that a little bit as the movie went on, to make sure he realized which was the "good" side and the "bad" side. At only 4 years old, it might have been easy for him to think the bullies were being glorified, OR that using your martial arts skills to hurt others is okay.
But with the proper supervision and guidance, and if you know your child and think you can address the issues, it was a good learning opportunity and chance to discuss values with your child. The right setting is also important - we wouldn't have taken him to a movie theater where it might have been more overwhelming or influential, and where we couldn't talk to him or pause the movie. We also reserved the right to turn it off if things went too far.
There are different concerns at different ages, which is why I rated it "iffy", but I wanted parents to know what a parent of a very gentle, sweet preschooler thought. It can be an okay movie for some younger kids.
What other families should know
Too much violence
Too much swearing
Great role models