In this paper we attempt to critically "make visible the flow and circulation of data" through analysing the datafication of the early years education sector in England (children aged 2-5). The concept of datafication is used to understand the processes and impacts of burgeoning data-based governance and accountability regimes. This analysis builds upon early childhood researchers who were influenced by Foucault and others, who have noted the ways in which the surveillance and performative culture of accountability both affirms, legitimates and seduces through discourses of quality while increasingly regulating and governing the early years. Using data from three research sites (a children's centre, a primary school and a combined nursery school and children's centre) as well as an interview with a local authority early years advisor, we examine how comparative data-based accountability increasingly governed early years teachers' professionalism and pedagogies. We argue that the planned tracking of children's performance from baseline assessment at four years old to eleven years old may further govern and constrain early years professionalism as young children are reconfigured as "miniature centres of calculation".