The children skiffed swiftly across the lake in their small boats.

skiffed 是动词 skiff 的过去式。skiff 指"用轻舟划行"，特指使用一种小型轻便的平底船（skiff）进行划行。这个词生动地描绘了孩子们用轻快的小船快速划过水面的场景。