Development of externalizing symptoms across the toddler period: The critical role of older siblings.

We examined child and family risk factors that were associated with the development of individual differences in externalizing problems across the toddler years. Our central hypothesis was that toddlers with more aggressive and disruptive older siblings would be at elevated risk for heightened levels of externalizing behavior. We tested this hypothesis in the context of other theoretically relevant risk factors: toddlers' inhibitory and...