The child threw himself into his mother's arms for comfort.

threw 是动词 throw 的过去式，throw 本意是"投掷、扔"，在这里引申为"快速移动身体"的动作。 into 是介词，表示"进入...内部"或"朝...方向移动"的状态。 threw himself into 这个短语形象地描述了孩子快速扑向母亲怀抱的动作。