This study investigated children's knowledge of double negation in Mandarin Chinese. Double negation is a phenomenon where two negatives cancel each other out, thereby yielding a positive meaning. Previous research found that children did not have knowledge of double negation until the age of seven or later. We argue that the observed difficulty of children in previous research is due to an artifact of the experimental task where the target structure was presented without the support of an appropriate context. To see whether preschool children have knowledge of double negation, we used experimental tasks which presented the structure in a plausible context. The results show that 5-year-olds already know that two negatives cancel each other out. By age 6 children are even able to produce double negation in an adult-like manner. This is evidence that double negation does not pose significant difficulty for young children if a plausible context is provided.