Teaching first graders is so often an utterly hit-or-miss proposition. I'll come up with a game or lesson plan that I think is a good idea, and it will be a flop. I'll be improvising, and suddenly have the best class ever.
Recently, with my Tuesday kids, I found an unexpected hit with the video and song, below. I had showed them a different youtube video, and they saw the icon for the little skeleton down in the corner, and were saying "해골 해골" ["skeleton skeleton"]. So I followed the link – maybe it was a good song?
Maybe they'd seen it in school or something. We watched video (and watched it again, and again, and again, because that's how it is with first-graders), and the look of concentration as they tried to follow along and say the words to the song was precious.