PYONGYANG, North Korea — Clapping, waving and even cracking a smile, the youngest son of North Korean leader Kim Jong Il joined his father Sunday at a massive military parade in his most public appearance since being unveiled as the nation’s next leader. Kim Jong Un, dressed in a dark blue civilian suit, sat next to his father on an observation platform at Kim Il Sung Plaza as armored trucks with rocket launchers and tanks rolled by as part of celebrations marking the 65th anniversary of the reclusive state’s ruling Workers’ Party. It was a momentous public debut for Kim Jong Un less than two weeks after he was made a four-star general and set on the path to succession, which would carry the Kim dynasty over the communist country into a third generation. His grandfather, Kim Il Sung, was the nation’s founder. Just days earlier, the world got a first glimpse of the son from photos published in a state newspaper. Sunday’s appearance was carried live by state TV, beaming him into North Korean households and giving the people their first good look at the future leader. Seeing the two Kims side by side above a huge portrait of…