In calculating children's thermal comfort, it is important to consider internal heat emissions, one of the main sources of which are the children themselves (heat exchange with the body surface, breathing, sweating). The accuracy of the calculation is influenced by their number, nature and intensity of activity, age, gender, and other parameters. Most regulatory documents base heat input calculations on a person with the following parameters: male, 20-30 years old, 70 kg, living in a temperate climate. This approach does not account for the physiological and age-specific characteristics of different age groups. The paper examines and refines the physiological parameters of children and uses models to numerically reflect the level of thermal comfort in a room. A calculation method is proposed that uses refined physiological parameters of children and evaluates thermal sensation of the indoor microclimate through the determination of Predicted Mean Vote (PMV) and Predicted Percentage Dissatisfied (PPD). Calculations of several microclimatic regimes were carried out, assessing the state of children of different ages and physical activity levels within the considered microclimate parameters. Analyzing the obtained data led to the conclusion that assessing human comfort using refined energy expenditures allows for a more flexible consideration of the thermal states of children in specific age groups. This enables higher quality regulation of the indoor microclimate of a specific room considering the examined factors.