Why prioritize 0-3?

In the first few years of life, more than 1 million new neural connections form every second. After this period of rapid proliferation, connections are reduced through a process called pruning, which allows brain circuits to become more efficient. In light of these findings, focusing on early childhood only makes sense. -Center for the Developing Child, Harvard University-

It is no surprise that the early childhood years are portrayed as formative. The supporting structures of virtually every system of the human organism, from the tiniest cells to the capacity for intimate relationships, are constructed during this age period. -National Research Council Institute of Medicine