The proposed research will study 150 Hispanic families at the time of the first teenage pregnancy and follow these families longitudinally at closely-spaced intervals across the teenager's transition to parenting. The focus of this research is on the development and adaptations of the other children within the household, or the pregnant teenager's siblings. The pregnant adolescents (n=150, ages 15-18), their 12-to 17-year-old younger siblings (n=240), and their mothers (n=150) will complete interviews and questionnaires when the teen is 7 months pregnant, 6 weeks postpartum, 6 months postpartum and 12 months postpartum to discern how family dynamics and children's developmental paths change under the stress of having an adolescent's infant join the household. Qualitative interviews will be conducted at 6 months postpartum on 40 randomly selected children to discern more narratively how their lives have changed after their sister gave birth. A comparison sample of 150 never-pregnant friends of the pregnant teens will also be studied across the same time period, along with their younger 12- to 17-year-old siblings and their mothers. The goals of this research are: (1) to identify the changes that occur (both immediately and across-time) within families that experience a teenager's birth; (2) to identify the family-level and individual-level factors that contribute to children's stress and maladaptation to these events, and conversely; (3) to identify the individuall level and family-level strengths and competencies that lead to children's successful adaptation to a sister's teenage birth. Outcomes include children's: acting-out problem behaviors (drug and alcohol use, precocious sexuality), internalizing symptomatology, academic motivation, and prosocial behavior. Growth curve models will be used to analyze across-time change and structural equation models will be used to analyze the mediating mechanisms that affect children's outcomes. The major significance of this research is its redress of the lack of knowledge about children's development in families experiencing an adolescent's birth and its ability to inform policy-makers about the salient issues facing children and families as adolescents transition to parenting.