Despite the abundance of research on neighborhoods' effects on children, most studies of neighborhood effects are cross-sectional, rendering them unable to depict the dynamic nature of social life, and obscuring important aspects of community processes and outcomes. This study uses residential histories from the Los Angeles Family and Neighborhood Survey and the Child Development Supplement of the Panel Study of Income Dynamics to explore two questions: 1) How much do residential mobility and neighborhood change contribute to the overall socioeconomic variation in children's neighborhoods? 2) Does measuring community factors at more than one point in time matter for the conclusions that we draw from research on "neighborhood effects" on children's behavioral, cognitive and health-related well-being? Residential mobility plays a non-trivial role over the period of childhood in determining children's exposure to neighborhoods of different economic types. However, quantitative estimates of neighborhood effects that allow neighborhood characteristics to vary through residential mobility and neighborhood change do not depict a strikingly different picture from cross-sectional estimates. Children do not experience enough variation in their local surroundings to produce meaningful differences between static and dynamic measurements of neighborhoods. We also uncover interesting regional and race/ethnic differences in neighborhood dynamics and neighborhood effects.