Transactional theories support that parent-child processes are best studied in conjunction with one another, addressing their reciprocal influence and change across time. This study tested a longitudinal, autoregressive model exploring bidirectional relations among maternal symptomatology, child internalizing/externalizing symptoms, and maternal sensitivity during the preschool period (child ages 3 to 5 years), comparing relations among families of typically developing children and children with developmental risk. This study included 250 families, 110 of which had a child with early developmental delay. Analyses utilized data from maternal report, father report, and observational methods. The results indicated significant stability in maternal symptomatology, child internalizing/externalizing symptoms, and maternal sensitivity over time. Support for bidirectional effects between maternal symptomatology and child internalizing symptoms was found specifically for mothers of children with developmental risk. Maternal symptomatology was found to mediate the influence of child internalizing and externalizing symptoms on maternal sensitivity. The findings underscore critical transactional processes within families of children with early developmental risk that connect increased maternal symptomatology to emerging child internalizing symptoms during the preschool period.