哄妹妹的英语可以说作 "to cajole one's pttle sister"。这个词来源于法语"cajoler"，意思是用甜言蜜语或者花言巧语来讨好某人。
例句：
He always knows how to cajole his pttle sister into doing what he wants. 他总是知道如何用甜言蜜语哄妹妹做他想让她做的事情。
She tried to cajole her sister into sharing her candy, but it didn't work. 她试着用甜言蜜语哄妹妹分糖吃，但是没有用。