Protest or pleasure? The response of first-born children to interactions between their mothers and infant siblings.

Triadic interactions between mother, pre-school age first-born, and 14-month-old second-born siblings were studied in 40 families as part of a longitudinal study using home observations. Interactions between mother and second-born exerted as important influence on the behaviour of the first-born; individual differences in the response of the first-born children were associated with difference in temperament of the first child, their reaction to the sibling birth, and with the sex of the sibling dyad. The age gap between siplings and the sex of sibling dyad influenced the time mother and second-born spent in interaction and the quality of this interaction.