put up for有关疑问

Among the most popular: paternity and kinship testing, which adopted children can use to find their biological relatives and families can use to track down kids put up for adoption.

这里的put up for adoption在这里是充当什么成分呢?

put up for adoption 为过去分词短语作定语修饰 kids。你一个人想想就应该了解的。