The little boy straddled the bench, swinging his legs.

straddled 是动词 straddle 的过去式。straddle 由词根 strad-（与"伸展"有关）和后缀 -dle（表示动作）组成，意思是"跨坐、叉开腿坐或站"，指双腿分开坐在某物上的动作。