Despite numerous critiques of the pioneering works of developmental child psychology, these key ideas continue to resonate within the field of ECEC (early childhood education and care). This article seeks to re-animate the critique through a closer look at two current tendencies within the Nordic countries: a growing and increasingly strict age segregation of kindergarten children; and a minor oppositional movement of family groups gathering children from one-to-six years of age. Looking towards Piaget as one of the main pioneers of developmentalism, we question whether strict age segregation is justified based on his theories -- a close re-reading of two of Piaget's major works would suggest not. Through reflections of kindergarten teachers working with age-homogeneous groups, we trace other discourses that developmentalism is entangled with. The analysis and deconstruction of the teachers' reflections point to the need to explore age segregation within a neoliberalist political context and further, show how this results in institutionalised othering. Through mobilising an agential realist reading we explore how narratives of kindergarten teachers that work with age-heterogeneous groups might inspire alternative ways of thinking/practising, and re-energise the critique of developmentalism.