This research examined how children's play varied as a function of the sex of the child, the sex of the play partner, and whether they played in dyads or groups. Children (mean age = 52 months) were observed during their free play. Data revealed that boys' same-sex play was more active-forceful, further from adults, and more stereotyped than girls' play, and that this pattern was generally exaggerated in groups versus dyads. Children rarely played only with children of the other sex (other-sex peers), but about one fourth of their interactions involved children of both sexes (mixed-sex peers). Compared with same- or dyadic other-sex play, mixed-sex play was more likely to occur near adults, and was intermediate in active-forceful and stereotyped activity choices. Findings confirmed that children's experiences in peer groups vary depending on the sex of the child and sex of play partners.