这种情况可以用中文称为“家长偏爱弟弟”，或者用英文表达为“parental favoritism towards the younger brother”。

这个短语的来源可能源自于家长对子女的偏见或偏心，通常是基于个人喜好或者其他原因，导致对一个子女的特别关注或帮助，而忽视或不关心另一个子女。

下面是一些例句：

The parents always gave the younger brother more attention and resources, leading to feepngs of resentment and jealousy in the older sister. (父母总是给弟弟更多的关注和资源，导致姐姐感到怨恨和嫉妒。)
Despite their efforts to treat both children equally, the parents couldn't help but show favoritism towards the younger son. (尽管他们努力平等对待两个孩子，但父母还是忍不住偏爱小儿子。)
The parents' favoritism towards the younger brother caused a rift in the family and damaged the relationship between the sibpngs. (父母对弟弟的偏爱导致家庭裂痕，损害了兄弟之间的关系。)