In the preschool period the central activity is play. Through play young children become able to differentiate meaning from objects and actions. Play is therefore a way for children to acquire a conscious relation to the world that is revealed in how they come to plan play actions and create shared imagination. We have argued, following Vygotsky’s ideas, that in play children bring the most intimate and personal aspect of their lives into the realm of social life, in the same way that adults may do through art. We have also discussed how children rework their experience in play and how this contributes to their acquisition of everyday concepts that are a foundation for their concept formation in school. Caregivers may help children benefit from play activities by providing them with experiences that they may rework in play. Nonetheless, if caregivers enter young children’s play, they should be aware of how children create lifeworlds in play that may be interrupted by newcomers. We also argue for assessing children’s social situation of development by focusing on activities and not abilities and present a method developed for this purpose.