The birth of a younger sibling can be a traumatic event for the older child. Unquestionably it places increased demands on parents and causes important changes in the inner balance of the family. Childrearing manuals are full of advice about how to get through this difficult time. But until now such advice has been based more on clinical guesswork than on direct observation of what really happens to families when a sibling is born.

With the arrival of Siblings, this gap in our knowledge is admirably filled. Judy Dunn and Carol Kendrick studied forty families for a...