general problems of the 2012 Nissan Armada

On or about 1/14/2015 I pulled into my mother's driveway to drop off my child for daycare. I put my vehicle in park, applied the emergency brake because the driveway sits up high, and turned off the Armada. Upon exiting my mother's house I observed my vehicle rolling off the driveway on it's own. It didn't stop until it hit the curb across the street. This could have lead to a crash or worse if I had been unloading my child from his carseat when the incident occured. I hate to think what would have occurred if one of my other children was standing behing the vehicle when the vehicle rolled off the driveway.