What a neat trip for a b-day present! Good going, Dad.
Make sure that you and your son keep hidden. I think one of the best ways to not catch any trout is to go stomping through the streams and spook all of the fish before you get to cast. Stay LOW, wear colors that blend into the surroundings, ie. browns, greens, dark colors, and remember that an 8" wild Smokey Mountian trout is a big fish! Also, hike at a minimum of 30 minutes before you start fishing. The longer you hike the better the fishing will be.