the elders（主语） become（系动词） burdens （表语）to be kicked around by their sons and daughters like a football（整个是不定式短语作后置定语,修饰表语 burdens
不定式短语分析：
to be kicked around(around 在这里是副词作状语修饰不定式to be kicked) by their sons and daughters （状语,by 引出动作的执行者）like a football（介词短语作方式状语）