The period of transition to adolescence is considered one of the key periods for the development of emotion regulation skills. Due to numerous developmental changes during this period, children can more flexibly use different emotion regulation strategies. Cognitive reappraisal and expressive suppression are two emotion regulation that develop intensively during adolescence. According to the models of emotion socialization, child’s emotion regulation is a mediator between different types of parental behaviors, including parental selfexpressiveness, and child’s psychological adjustment. In those models, children's individual characteristics, such as environmental sensitivity, are positioned as potential moderators of parental effects. This moderating role of environmental sensitivity is well described within the environmental sensitivity framework. According to this framework, children vary in their susceptibility to different external and internal stimuli. Compared to low-sensitive children, high-sensitive children are hypothesized to be more prone to negative effects in unfavorable contexts, but they also stand to gain more in favorable contexts. The role of the mother’s and father’s positive and negative expressiveness in the development of children’s cognitive reappraisal and expressive suppression use is insufficiently examined in prior studies. Similarly, there is a need for further studies that would explore links between children’s emotion regulation and adjustment during the transition to adolescence while considering their temperamental characteristics. The aim of this study was to examine the full emotion socialization model, with changes in children’s usage of cognitive reappraisal and expressive suppression as mediators between mothers’ and fathers’ expressiveness and changes in children’s emotional and behavioral problems during the transition to adolescence. It was also explored whether children’s environmental sensitivity moderates links in the aforementioned model. This study was conducted as part of the Child Well-being in the Context of the Family project (CHILD-WELL), financed by the Croatian Science Foundation (IP-2019-04-6198). It was a two-wave study spanning one year with 728 mother-father-child triads. Children (45.7% boys) were aged between 8 and 13 years in the first wave. In both waves, children provided data about their own habits of using two emotion regulation strategies (cognitive reappraisal and expressive suppression), environmental sensitivity, and their levels of emotional and behavioral problems. Parents gave information about their own expressiveness within the family in the first study wave. After data cleaning, the main hypotheses were tested by employing both structural equation modeling and path analysis depending on the model complexity. Predictive effects of parental expressiveness were examined at the family level by employing the common fate model, as well as separately for each parent. Hypothesized models were tested in three main steps. Firstly, parental expressiveness was examined as a predictor of changes in children’s emotion regulation strategies. Secondly, it was explored whether emotion regulation strategies measured at baseline predicted changes in emotional and behavioral problems. Thirdly, whole mediational model was tested with emotion regulation use in second wave as a mediator between parental expressiveness and changes in emotional and behavioral problems. Environmental sensitivity was examined as a moderator of all direct and indirect effects. The results showed that positive and negative parental expressiveness in the family context did not predict changes in children’s cognitive reappraisal and expressive suppression. There were no individual effects for mothers or fathers in the prediction of the two child emotion regulation strategies. Furthermore, children’s environmental sensitivity did not moderate the parental effects. There were also no longitudinal links between emotion regulation strategy usage and changes in emotional and behavioral problems, nor were those links moderated by environmental sensitivity. However, there was a small positive longitudinal link between emotional and behavioral problems measured at baseline and changes in expressive suppression. Children with higher emotional and behavioral problems at baseline had increases in expressive suppression a year later. Next, in this study, we did not find moderated indirect effects between parental expressiveness and changes in children’s emotional and behavioral problems, through changes in emotion regulation at different levels of a child’s environmental sensitivity. Changes in expressive suppression and cognitive reappraisal were expectedly linked to changes in emotional and behavioral problems. Decreases in reappraisal and increases in suppression were linked to increases in emotional and behavioral problems. Environmental sensitivity moderated only the direct link between positive parental expressiveness and changes in emotional and behavioral problems and the link between expressive suppression measured at the second wave and changes in emotional and behavioral problems. Only for children with high levels of environmental sensitivity, there was a negative link between family-level positive expressiveness and changes in emotional and behavioral problems. Compared to low-sensitive children, highly sensitive children whose parents had high positive expressiveness experienced lower total problems a year later. The father’s positive expressiveness showed a similar pattern of interactive effect with environmental sensitivity in the prediction of emotional and behavioral problems. Lastly, compared to low-sensitive children, for high-sensitive children, there was a stronger positive link between expressive suppression measured at the second wave and changes in emotional and behavioral problems. Patterns of significant interaction effects support the differential susceptibility model according to which highly sensitive children have more positive outcomes in positive contexts and more negative outcomes in negative contexts. Overall, this study did not provide evidence about the importance of parental expressiveness in two-parent families for the development of cognitive reappraisal and expressive suppression during the transition to adolescence. This result should be cautiously interpreted while considering selection bias. Similarly, this study does not provide enough evidence about the direction of prospective links between emotion regulation strategy usage and psychological adjustment. However, changes in both emotion regulation strategies were consistently linked with changes in psychological adjustment. Although these results do not allow for causal interpretations, they demonstrate consistent interrelatedness of changes in mental health and behaviors used to modulate emotions. Lastly, this study supports differential susceptibility model and points to the importance of considering child characteristics in developmental models.