Pokemon Diamond DS - Stuck in First Room at Start of Game

I just got Pokemon Diamond game for the DS for my 5-year-old son. I played Pokemon a long time ago for the Game Boy Color and still do some gaming, so I'm not a novice. Either something is wrong with the game or we are doing something very basic wrong. We are stuck in the very first room - right after we started the game. There's a PC in the room, a TV, and a bed. When we walk to the edge of the screen, it is black and an invisible wall stops us from moving any further. It looks like the dark area should just open up & let us walk into it but it just stops us cold. So, we are stuck in this one room roaming around in circles. There's no door or anything that I can see to get us out of here. There's nothing in the instructions about how to resolve this. Thanks so much & sorry if we've missed the nose in front of our face.