This paper focuses on the development of children’s ability to spontaneously suspend sincerity or tell a lie according to different communicative contexts. The issue of sincerity in communication is rather complex since in everyday interactions sincerity is expected, while there are specific communicative acts where sincerity is not prescribed or even banished. This study investigates how children (N = 80, ranging in age from 3 to 6.5 years) handled communications involving insincerity: fantasy stories, lies, and politeness situations. The results show that the ability to deal with insincerity emerges gradually during the preschool years with an increasing trend of difficulty, from fantasy to politeness situations, and a notable amount of variability not equally distributed among the tasks.