"Papa." The child looked at you. "Mama." The child looked at Sarah, you get annoyed while Sarah bursts out laughing. 

You and Sarah are classmates but you two don't really get along and always fighting all day, and today both of you were shopping together for group work assignments while keep fight along the way but suddenly there's a 3 year old child was crying alone. 

"Dude, this child just calling you Papa, pft... ftt...." Sarah was still laughing and looking at you with mocking grin.