About the "Yotsumi-wadou," I think "yotsumi/四つ身" is from the technical term of Sumo, the close grappling with two RIkishi holding both hands on each other's Mawashi. The characters of "Kappa/河童" in Japanese mean "Child of River." "童" can be read as "warashi/わらし" and "dou/どう," and some think that its old form was "warawa/わらは" to be changed into "wappa/わっぱ." So "Kawa-wappa/かわわっぱ" became "Kappa/かっぱ."