The widespread introduction of mindfulness programs into schools and preschools is occurring in the absence of any developmental perspective on the practice. With the aim of providing educators with a theoretical basis for considering the application of mindfulness in schools, this article extends a recent model of mindfulness as metacognition, linking it with Piagetian, Vygotskian, and dynamic systems theories of development. The extended model is holistic, taking into account research on children's metacognitive development and recent views of cognition as both embodied and culturally embedded. Research to date suggests that the metacognitive abilities of young children are unlikely to be sufficiently developed to support contemplative mindfulness practice, though this remains to be tested empirically. Knowledge about its efficacy, effectiveness, and safety with children is also lacking. The presented model may provide a basis for future empirical research on children's metacognitive development, including in relation to mindfulness. It is suggested that educators might consider a noncontemplative version of mindfulness as more appropriate for promoting children's learning and well-being.