Diarrheal diseases remain a leading cause of morbidity and mortality among children under five years of age, particularly in low-resource settings. This study, conducted in Kosti, Sudan, in 2014, aimed to assess the prevalence, risk factors, and health outcomes associated with diarrheal illnesses in this vulnerable population. A cross-sectional survey was carried out involving 384 caregivers of children under five, selected through systematic random sampling from households across urban and peri-urban areas of Kosti. Data were collected using structured questionnaires and analyzed to identify key determinants such as water, sanitation, hygiene (WASH) practices, feeding patterns, and healthcare-seeking behaviors. The findings revealed a high two-week prevalence of diarrhea (approximately 22%), with significant associations observed between diarrheal episodes and inadequate access to safe drinking water, poor sanitation facilities, lack of handwashing with soap, and early cessation of breastfeeding. Children from households with lower socioeconomic status were disproportionately affected. The study underscores the urgent need for integrated public health interventions targeting WASH infrastructure, maternal education, and community-based health promotion to reduce the burden of diarrheal diseases among under-five children in Kosti. These results provide valuable evidence to inform local and national policies aimed at achieving child health targets under the Sustainable Development Goals.