also: ぽんぽんせん
noun
pop-pop boat; toy steam boat
A toy boat propelled by a simple steam engine, often a candle-heated boiler with a small exhaust pipe that makes a popping sound.
子供の頃、ポンポン船をお風呂でよく遊ばせた。
When I was a child, I often played with a pop-pop boat in the bathtub.
Standard katakana-kanji spelling.
Hiragana variant; less common but still used.
From the popping sound (ポンポン) the toy makes, plus 船 (boat).