Children are good at interacting with and exploring new situations. Probably at first sight, children’s behaviors may seem chaotic, a matter of trial, error, changing from time to time. But in fact their behavior is creative. But what are the main characteristics of their interactions and reasoning when children work in dyads? For instance, are the children willing to collaborate when the tasks become more difficult, or will they prefer to copy the solution of their partner or decide to work independently? This thesis explores the dynamics of interaction and reasoning of dyads of preschoolers during problem solving situations. By using challenging hands-on tasks about physics (air pressure and inclined plane), the aim of this thesis was to identify the regularities of children’s actions and verbalizations over the long term. Beyond the success and failure of children’s performances, the studies focused on the behavioral changes of overtime. The main findings indicate that during problem solving situations (1) preschool children are likely to work independently rather to collaborate, and (2) they are able to use complex reasoning skills such as descriptions, predictions and explanations. In addition, (3) children´s actions aimed at solving a task are more complex that their explanations regarding how to solve the task, and (4) preschool children are able to transfer knowledge to a new challenging situation, based on their previous experiences with a task. Next time you watch children playing together, please remember that interesting things are happening in their young minds.