How can we solve the paradox of false-belief understanding: if infants pass the implicit false belief task (FBT) by nonverbal behavioural responses why do they nonetheless typically fail the explicit FBT till they are 4 years old? Starting with the divide between situational and cognitive accounts of the development of false-belief understanding, we argue that we need to consider both situational and internal cognitive factors together and describe their interaction to adequately explain the development of children’s Theory of Mind (ToM) ability. We then argue that a further challenge is raised for existing accounts by helping behaviour versions of the FBT. We argue that the common two-stage accounts are inadequate: we need to allow for three central stages in a continuous development. Furthermore, drawing on Perner et al.’s (Cognition 145: 77–88, 2015) and Perner and Leahy’s (Review of Philosophy and Psychology 7 (2): 491–508, 2016) recent mental files account, we provide a new account of the development of these three stages of ToM ability by describing the changes of the structure and organisation of mental files including the systematic triggering role of types of situations. Thereby we aim to establish a situational mental file (SMF) account as a new and adequate solution to the paradox of false-belief understanding.