"Mary thinks that John thinks that…" Developmental change and individual stability in attributing second-order mental states in 5 to 7-year-olds.

Second-order understanding of mental states develops during middle childhood. However, due to the limited number of longitudinal studies on this topic, the timing of developmental changes and the stability of individual performance remain insufficiently explored. The current study examined the development of recursive theory of mind abilities, namely second-order ignorance and false-belief understanding, between the ages of 5 and 7. Using the Ice Cream Task and the Birthday Puppy Task, we longitudinally tested 166 Polish children at three time points (mean ages: MT1 = 5.64 years, SDT1 = 0.23; MT2 = 6.69, SDT2 = 0.11; and MT3 = 7.63, SDT3 = 0.13). Although we observed overall growth in second-order mental state understanding, understanding of ignorance emerged two years earlier, showing smaller gains between ages 5 and 7 compared to false-belief understanding. Moreover, most children demonstrated consistent developmental trajectories in individual performance. These findings provide a comprehensive developmental overview of second-order mental state attribution, suggesting that, alongside gradual improvement, the observed rank-order stability in rToM may reflect partially stable individual differences over time.