The relationships between child vulnerability to stress, birth order, and stage of family development were assessed. Four stages were identified: Stage I involves 2 parents and their 2 or 3 natural children; Stage II, following divorce, involves mother and her 2 or 3 natural children; Stage III following remarriage, involves mother, stepfather, and mother's 2 or 3 natural children; and Stage IV involves mother, stepfather, mother's 2 or 3 natural children from her first marriage, and the single child from her current marriage. In general, vulnerability of first borns and last borns shifted across stages in a complementary fashion. First borns were most vulnerable in Stage III, least vulnerable in Stage IV, and at intermediate levels in Stages I and II. Last borns were most vulnerable in Stage IV and least vulnerable in Stage HI. The results were interpreted in terms of a linkage between emotional symptoms, gains and losses in privileged positions in the family, and changes in mother‐child closenes