Adverse experiences superseding a child's capacity to sustain regulation of emotion and adaptive function are theorized to constitute "toxic stressors" when they induce a deleterious biological response within an individual. We ascertained presumptive parameters of toxic stress among 164 low-income infants and toddlers (ages 4-48 months) from 132 families enrolled in Early Head Start (EHS). We randomized a subset of these families into a pilot intervention arm of parenting education (the Incredible Years, TIY), which supplemented the EHS curriculum. Official report child abuse and neglect (CAN) and child behavior were serially ascertained over the course of the study. We observed relatively low associations among maternal depression, CAN, caregiver-child relationship quality, hair cortisol, and adverse child behavioral outcomes. Moreover, despite poverty and the high prevalence (51%) of CAN in this sample, the frequency of clinical-level internalizing and externalizing behavior among the children did not exceed that of the general population, by their parents' report. The pilot supplementation of EHS with TIY improved attendance in group meetings but did not significantly reduce adverse behavioral outcomes or CAN. This study revealed marked independence of standard indices of toxic stress (child maltreatment, maternal depression, caregiver emotional unavailability) which have been presumed to be risk factors for the development of psychopathology. That they were weakly inter-correlated, and only modestly predictive of child behavioral outcomes in this EHS sample, caution against presumptions about the toxicity of individual stressors, highlight the importance of ascertaining risk (and compensatory influences) comprehensively, suggest buffering effects of programs like EHS, and demonstrate the need for greater understanding of what parameterizes resilience in early childhood.