This paper reports the pilot part of a study investigating the development of the expression of communicative intents of Japanese children interacting with their caregivers. The main purpose of this pilot was to identify and describe developmentally different features of children’s communicative acts in relation to mothers’ communicative acts. Ten children, of ages ranging from 11 months to 28 months and their mothers, participated in this pilot. Each mother / child dyad was observed in the two semi-structured contexts of joint book reading and toy play. The joint book reading refers to the activities where the dyads interacted with picture books and toy play refers to the activities where they interacted with given toys. Analyses were made of both mothers’ and children’s communicative acts including both gestural and speech activity, using an existing coding system called the Inventory of Communicative Acts-Abridged (INCA-A) with an additional supplemental coding system. The results indicate that the adopted coding system seemed to capture developmentally different features of communicative acts in terms of quantity and quality. Examinations of the mothers’ communicative acts also suggested possibilities of identifying different interaction styles across dyads as well as changes within a dyad in which mothers deploy a variety of communicative acts in relation to their child’s developmental course.