Play is a predominant individual and social activity of early childhood and has been related to young children's early cognitive growth, social development, and preparation for formal schooling. We examined individual differences and developmental changes in South Korean child and mother exploratory and symbolic play longitudinally when children were 13 and 20 months of age. Children engaged in less exploratory and more symbolic play when playing collaboratively with their mothers than when playing alone. Children engaged in more symbolic play at 20 months than 13 months. Child solitary and collaborative symbolic play was modestly stable across time, but child exploratory play and maternal play were not. Child solitary and collaborative symbolic play were correlated across the two ages. Child and mother play were regularly associated at the two ages, and 13-month maternal play predicted 20-month child collaborative play. The cross-cultural validity of play is affirmed, and individual differences and age-related changes in child and mother play are partly mediated by matched partner play and partly motivated by processes independent of partner play.