The importance of the parent-child relationship during early childhood (i.e., 0-5 years) on children's socioemotional functioning has been extensively documented in the literature. However, limited work has examined the degree to which dyadic features of the parent-child relationship changes over the course of early childhood and whether growth in these features relate to children's functioning. The present study aimed to address this limitation by examining change trajectories of dyadic affective mutuality and mutual enjoyment during the first 2 years of life and whether these trajectories were associated with child problem behavior at age four. The sample was comprised of 374 low-income, infant-mother dyads recruited for an efficacy trial of a tiered parenting program designed to promote school readiness. Affective mutuality and mutual enjoyment were assessed via coded interaction tasks between mothers and their infants at 6, 18, and 24 months. Mothers reported on children's internalizing and externalizing problem behavior at 48 months. Results from latent growth curve analysis revealed dyads' affective mutuality significantly increased, and mutual enjoyment significantly decreased, from 6 to 24 months. Initial levels and positive change in affective mutuality from 6 to 24 months were both negatively associated with child internalizing problems, but not externalizing problems, at 48 months. These findings emphasize the importance of conducting work that conceptualizes the dyad as the unit of study and explores how changes in the parent-child relationship may themselves be important indicators for children's future functioning.