Early childhood education (ECE) institutions may be one place for young children to obtain a significant proportion of their daily physical activity (PA). Even though young children are generally considered to be very active, and recess time is considered an important environmental factor for promoting PA, evidence suggests that young children spend most recess time participating in sedentary activities. To our knowledge there have been no systematic evaluations of the PA levels and patterns during recess time in Spanish preschool children. Therefore, the aims of this study were threefold: (a) to analyse the PA patterns and sedentary behaviour during recess time in outdoor ECE environments through accelerometry and systematic observation in a sample of Spanish preschool children; (b) to validate the use of the Observational System for Recording Activity in Children – Preschool (OSRAC-P) to assess PA levels, using accelerometry as the reference method; and (c) to evaluate personal, psychosocial and environmental correlates of moderate to vigorous PA (MVPA) and sedentary behaviour in young children during recess. Our major findings were that: (a) young children engaged in very little MVPA during recess; (b) boys were significantly more active than girls; (c) younger preschoolers were more active than older preschoolers; (d) social interaction was a positive predictor of MVPA levels; and (e) direct observation through OSRAC-P is a reliable system to characterize PA patterns in young children. These findings indicate the need to increase MVPA in ECE institutions during break-times and have implications for the ECE community, especially for practitioners, preservice practitioners and health professionals.