This handbook is a guide and reference document for those researching the child data files of the 1986-1990 National Longitudinal Survey of Youth, sponsored by the Bureau of Labor Statistics. It describes the child data collection procedures, the nature of the child sample, the child data files available, and the specifics of the child assessments included in the 1990 survey. Outside resource documents, internal analyses, and data caveats are also provided for each assessment. A variety of statistical materials are provided to help users decide whether data are appropriate for their research objectives. Section 1 provides an overview of the children in the survey. Section 2 gives technical information on survey design, field work, representativeness of the sample, and the data processing. Section 3 describes the mother and child sample and highlights the strengths and limitations of the data set. Section 4 describes the child data files (available on magnetic tape or CD-ROM), and the behavioral and attitudinal data available on the children and their families. Section 5 focuses on the criteria for selecting the child assessments and then describes the child data collection from 1986 through 1992. Section 6 describes the child data files, their documentation, and the primary components of the main youth documentation, along with suggestions for their access and management. Most sections include statistical tables and lists of supplemental documentation and publications. Appendices with survey instruments and tables of raw scores are included. (TM)