Laughter and smiling are frequently experienced in social settings, yet more research is required to delineate their development and dynamics. We investigated toddlers' and parents' shared positive expressions in playful interactions. We observed eighty 30-month-old toddler-parent dyads in two phases of 8 min in length. In each, one person was asked to make the other laugh (parent phase) or to show how much fun they were having (child phase). Using the facial action coding system (FACS), we coded the temporal occurrence and intensity of Duchenne displays (smiles and laughs) and non-Duchenne displays (e.g., social smiles) for toddlers and parents. We then applied cross-recurrence quantification analysis, which showed that shared positive expressions were present. Smiles and laughter were initiated by both parents and toddlers. Further, using Shannon entropy, parents' and toddlers' variability in smile and laughter intensity was predictive of shared positive expressions. Finally, parents' and toddlers' smile and laughter intensities were strongly and positively associated. Overall, our study showed that experiencing, initiating, and dynamically expressing smiles and laughter develop early and are settled within interactive frames.