The children's faces were full of animation as they played in the playground.

animation 来自动词 animate（使有生气、使活泼），名词形式表示"活力、生气勃勃的状态"。词根 anim- 源自拉丁语，意思是"生命、灵魂"，后缀 -ation 表示动作或状态。animation 在这里形容孩子们脸上充满生命力的表情。