As medieval writers recognized, early childhood is a slow, awkward, errant developmental process. It is also witness to a vital human ecology. This talk will take a relatively methodological cast in identifying powerful conceptual resources that come from studying medieval embryology, infancy, and childhood. For medieval writers preoccupied with the formation of the child (as with other kinds of material causation), one must reckon with a volatile, precarious if also precious moment of creaturely life when things are barely human. I will discuss both instructional and literary texts (e.g., The King of Tars and Sir Gowther).