Isekai Ouji no Toshiue Cinderella

Rika was suddenly summoned to another world to become the prince's bride. However, the prince is only 11 years old! Rika expresses her displeasure, but gradually bonds with the prince who loves her. As she looks for a way to return to her own world, Rika decides to watch over the prince's growth with sisterly affection. And so a life with the prince begins!

(Source: AlphaPolis, translated)