Introduction: A child's early development is largely determined by environmental influences. Through a transactional model of knowledge transmission, children adopt cultural specificities of the environment (such as language and the use of objects), and the main mediators in the transmission of knowledge about the world are adults. Imitation of others is a highly effective learning mechanism in early development. However, children do not imitate everything they see and hear, but rely on communication and social cues to help them imitate and select what is worth imitating. When adults communicate with children, they change the characteristics of their communication - both their speech and the movements they make. These behaviours are referred to in the literature as child-directed behaviours. Child-directed behaviours are specific to interactions with children and differ from speech and movements directed at adults. Studies have shown that child-directed behaviours increase the child's attention and interactivity, improve the processing of stimuli, and promote learning. However, in the literature they are considered as two separate constructs – child-directed speech (CDS) and child-directed actions (CDA). The mechanisms of their influence on different behaviours in children are not yet well understood. The literature on the influence of child-directed behaviours on imitation is sparse. There are no studies on whether CDS and CDA have a differential impact on imitation overall and how they specifically affect imitation in different modalities (verbal imitation vs. imitation of actions with objects). The extent to which their synchronised use contributes to the occurrence of imitation in the child has never been investigated. Therefore, the main aim of this study was to investigate the individual effects of CDS and CDA and their synchronised occurrence on imitation of actions with objects and the occurrence of verbal imitation in children aged 18 months. Methodology: The design of this study corresponds to a complex experimental design with independent groups. The study included typically developing children aged 18 months (N=120) randomly divided into four groups of the same age and gender. There were thirty children in each group. All groups were presented with tasks to imitate actions objects from the Frankfurt imitation test (Kolling & Knopf, 2015), but the tasks were presented to each group in one of four ways: with neutral presentation (NP), presentation with CDS, presentation with CDA, and presentation with joint CDS and CDA. The children were given a total of 14 tasks comprising between one and six steps. The total score, which represents the sum of the correctly performed steps in all tasks, was a measure of the imitation of actions with objects. The measure of verbal imitation was represented by the sum of occurrences of verbal imitation during the performance of all imitation tasks with objects. Results: The results clearly showed that the children's success in imitating actions with objects and the frequency of occurrence of verbal imitations differed significantly between the children in these four task presentation conditions (p<0,01). More detailed analyses provided answers to the specific research objectives. The first specific aim of the study was to examine whether CDS and CDA separately influence imitation of actions with objects and the occurrence of spontaneous verbal imitation in relation to a situation without child-directed behaviours (neutral presentation). The results showed that children aged 18 months correctly imitated a greater number of tasks with objects when the tasks were presented with some form of child-directed behaviour (either CDS or CDA), and that spontaneous verbal imitations also occurred more frequently when the tasks were presented with any form of child-directed behaviour compared to the condition without CDS and CDA. Large effect sizes were found, i.e. that there was a considerable influence of child-directed behaviours on imitation compared to a neutral presentation. The second specific aim was to investigate the extent to which the synchronised use of CDS and CDA influences the child's imitation of actions with objects and verbal imitation. The tests conducted revealed a significant difference in the imitation of actions with objects and the occurrence of verbal imitation, in the sense that the children imitated more accurately in a situation in which both child-directed behaviours were present (CDS+CDA) than in a situation in which only one child-directed behaviour (CDS only or CDA only) was present. The effect size was also large. The third specific aim was to determine the possible differential influence of CDS and CDA on the imitation of actions with objects and on the occurrence of verbal imitation. It was predicted that the presence of CDS and CDA in task presentation would have a differential influence on imitation of actions with objects and verbal imitation, with the presence of CDS having a greater influence on the frequency of verbal imitation and the presence of CDA having a greater influence on imitation of actions with objects. However, there were no differences in the influence of CDS and CDA on the imitation of actions with objects or on the occurrence of verbal imitation, although a slightly greater effect of CDS than of CDA was observed for verbal imitation. The results obtained were interpreted in the context of knowledge about early learning, such as understanding other people's intentions, preferences in imitation, segmentation of words and actions, and processing of multimodal information. Conclusion: This study provided a systematic review of the influence of child-directed behaviours on imitation in two modalities in children aged 18 months. It contributed to a better understanding of the environmental mechanisms that contribute to social learning in young children. In addition, it provided a basis for further research into early interactions and early learning, and practically for the development of interaction strategies that promote learning in children at an early age.