Here's a great video on the benefits of rough-housing with your children. I believe that many of these can also be attributed to martial arts training with children.
The past few years martial arts and "rough" play have gotten bad reputations. I suppose some parents would rather have their children play violent sociopathic video games like Grand Theft Auto than have them engage in physically active, morally based training with lifelong benefits. That'll be another blog entry on its own.
For now, simply enjoy the video on the benefits of rough-housing.