What is the ruling on teasing my younger sister by telling her things that did not happen to bring joy to her heart, when she knows that?

Lying to a younger sister is not permissible, as lying to children is the same as lying to adults. There is a hadith that warns against lying, even in jest. However, lying is permitted for the purpose of giving parables or stories that aim to teach good morals, such as courage. Nevertheless, it is preferable to completely avoid it so that children do not become accustomed to it.