A great change is coming over childhood in the world's richest countries. Today's rising generation is the first in which a majority are spending a large part of early childhood in some form of out-of-home child care. At the same time, neuroscientific research is demonstrating that loving, stable, secure, and stimulating relationships with caregivers in the earliest months and years of life are critical for every aspect of a child’s development. Taken together, these two developments confront public and policymakers in OECD countries with urgent questions. Whether the child care transition will represent an advance or a setback for today's children and tomorrow's world will depend on the response.