SECCYD is a prospective, longitudinal study following the development of over 1,000 children from birth to age 26 and their families. Participants were recruited in 1991 from 24 hospitals in 10 different cities across varying states of the United States. Over 1,300 families with full-term, healthy newborns were enrolled and completed a home interview when the infant was 1 month old. Participants and their families were studied at 14 major assessment ages in the child's development, which were organised in six phases. At birth, the recruitment sample was 52% male and 24% minoritized children, with 10% of mothers not having completed high school and 15% being single mothers. Mothers had an average of 14.2 years of education, and the average family income was 3.6 times the poverty threshold.