Infant brain development is a dynamic process dependent upon endogenous and exogenous stimulation and a supportive environment. A critical period of brain and neurosensory development occurs during the third trimester and into the "fourth" trimester (first three months of life). Disruption, damage, or deprivation in the infant's social and physical environment can create permanent deficits in the developing neurosensory systems. Implications for infant child care environments are discussed, and a review of quality and standards in infant child care environments leads to a call for improvements to optimize child development.