Drawing from developmental psychology and psychopathology, we propose a new, developmentally informed approach to parenting interventions that focuses on elucidating changes in the unfolding developmental process between the parent and child. We present data from 186 low-income mothers of toddlers, randomly assigned to a child-oriented play group or a play-as-usual group. We examined the maladaptive cascade from child difficulty to mother adversarial, negative parenting to child maladjustment, well documented in the literature. The measures incorporated multiple observations and reports. As expected, the sequence from child difficulty (pretest) to mother adversarial, negative parenting (Posttest 1, after 3-month intervention) to child maladjustment (Posttest 2, 6 months later) was present in the play-as-usual group, but absent, or defused, in the child-oriented play group. The findings are consistent with a view of intervention presumably enhancing the mother–child relationship, which in turn served to moderate future mother–child dynamics, altering its otherwise anticipated negative trajectory. A closer examination of the cascade revealed that, at Posttest 1, mothers in the play-as-usual group engaged in more adversarial, negative parenting (controlling for pretest) than did mothers in the child-oriented play group when their children were of high difficulty. The intervention appears to exert its primary influence on the cascade by weakening the link between child difficulty and maternal adversarial, negative parenting.