This study investigates the effects of age and prior experience with age-mates on attachment behavior and exploratory play with another child. Twenty home-reared children, half between 18 and 24 months and half between 24 and 30 months, and 20 day care children, also equally divided into the two age groups, were observed in the Ainsworth strange situation. The stranger was a 5-year-old female. The arrangement of the playroom was modified to create a forced-choice situation between the mother and a playmate and/or toys. Repeated measures of exploration and attachment behaviors were analyzed by computing multivariate analyses of variance and covariance. Age of the children affected exploratory and attachment behavior. Older children ventured a greater maximum distance from the mother and exhibited less crying associated with separation from the mother. Day care children ventured a greater maximum distance from the mother, spent more time away from the mother, more time out of mother's visual field and more time in exploratory play. No differences in intensity of attachment behavior at reunion attributable to rearing situation were found. Home-reared and day care children did not differ in the amount of time spent in social play. Significant rearing by sex interactions led to consideration of the differential effects of the rearing situations for boys and girls. (Author/RH)