theory of mind plays a fundamental role in human social interactions. people generally better understand the mental states of members of their own race, a predisposition called the own-race bias, which can be significantly reduced by experience. It is unknown whether the ability to understand mental states can be similarly influenced by own-age bias, whether this bias can be reduced by experience and, finally, what the neuronal correlates of this processes are. We evaluate whether adults working with children (WC) have an advantage over adults not working with children (NWC) in understanding the mental states of youngsters. Participants performed fMRI tasks with Adult Mind (AM) and Child Mind (CM) conditions based on the Reading the Mind in the Eyes test and a newly developed Nencki Children Eyes test. WC had better accuracy in the CM condition than NWC. In NWC, own-age bias was associated with higher activation in the posterior superior temporal sulcus (pSTS) in AM than in CM. This effect was not observed in the WC group, which showed higher activation in the pSTS and inferior frontal gyri in CM than in AM. Therefore, activation in these regions is required for the improvement in recognition of children's mental states caused by experience. Humans are social beings, and therefore, the ability to understand the mental states of others is crucial to everyday life and to adequately function in modern society, especially regarding social interactions. This ability is called theory of mind (TOM) or mentalizing. TOM allows us to accurately understand and predict the goals, beliefs, desires and emotions (together described as mental states) of others 1-3. TOM can be divided into the socio-perceptual component, referring to decoding or detecting other's mental states based on perceptual information (e.g. a photograph of the eye region) and the socio-cognitive component allowing to infer about others' intentions or beliefs based on their behaviour and one's knowledge about the world 4,5. Another distinction described in the literature divides TOM into affective and cognitive TOM 6. Affective TOM refers to an ability to infer about feelings of others, while cognitive TOM allows inferring about beliefs. Several studies showed the own-race bias in socio-perceptual component of TOM 7-9-a tendency to better recognize mental states of members of the same race. At the same time, the own-race bias could also be observed in less complex processes, such as face recognition (correctly recalling and matching known vs unknown faces) 10. A similar phenomenon, called the own-age bias, causes the attention to focus on faces of people the same age 11-13