Exposure to fecal pathogens contributes to childhood diarrhea and stunting, causing harmful short- and long-term impacts to health. Understanding pathways of child fecal exposure and nutritional deficiencies is critical to informing interventions to reduce stunting. Our aim was to explore determinants of latrine use, disposal of child feces, and perceptions and provisions of a safe and clean child play environment among families with children under two (CU2) years to inform the design of a behavior change intervention to address water, sanitation, and hygiene (WASH), and nutrition behaviors. In 2016, we conducted a mixed-methods formative research in western Kenya. We conducted 29 key informant interviews with community leaders, health workers, and project staff; 18 focus group discussions with caregivers of CU2 years; and 24 semi-structured household observations of feeding, hygiene, and sanitation behaviors. We used the capability, opportunity, motivation, and behavior model as our theoretical framework to map caregiver behavioral determinants. Latrine use barriers were lack of latrines, affordability of lasting materials, and social acceptability of unobserved open defecation. Barriers to safe disposal of child feces were lack of latrines, time associated with safe disposal practices, beliefs that infant feces were not harmful, and not knowing where children had defecated. Primary barriers of clean play environments were associated with creating and maintaining play spaces, and shared human and animal compounds. The immediate cost to practicing behaviors was perceived as greater than the long-term potential benefits. Intervention design must address these barriers and emphasize facilitators to enable optimal WASH behaviors in this context.