Previous research investigating the relationship between language proficiency and iconic gesture use has produced inconsistent findings. This study investigated whether a linear relationship was assumed although it is a quadratic relationship. Iconic co-speech gesture use by 4- to 6-year-old French–Japanese bilinguals with two levels of French proficiency (intermediate and low) but similar levels of Japanese proficiency was compared with that of high-proficiency French monolinguals (Study 1) and Japanese monolinguals with similar proficiency to the bilinguals (Study 2). To control the information participants communicated, a dynamic referential communication task was used; a difference between two cartoons had to be communicated to an experimenter. Study 1 showed a significant quadratic relationship between proficiency and iconic gesture use in French; the intermediate-proficiency bilinguals gestured least among the three proficiency groups. The monolingual and bilingual groups with similar Japanese proficiency in Study 2 gestured at similar rates. It is suggested that children gestured for different reasons depending on their language proficiency and the cognitive resources available for the task.