This study was intended to examine the relationship between children's shyness and play behaviour during peer play, and the moderating effect of the level of children's language development. Participants were 229 South Korean children aged 48-53 months. The results of the study are as follows. Children's shyness was negatively associated with their positive play interactions and positively associated with their play disconnection. Children's receptive language skills moderated the relationships between their shyness and positive play interactions, as well as between their shyness and play disconnection. However, their expressive language skills did not work as a moderator. The findings of the study indicate that receptive language helps shy children join peer play better than expressive language does, because verbal conversations only become more important later in childhood. Interventions for shy children, particularly those with low language skills, should be tailored to improve their receptive language abilities.