This study tested the effect of a 4-week Water, Sanitation, and Hygiene (WaSH) intervention on diarrhoeal infections in children, and knowledge, awareness, practices (KAP) in the six tribal villages of Palghar. We performed a quasi-experimental study in N = 180 households among mothers with children under-five registered in the anganwadi centers. Households received either WaSH kits (control arm n = 90) or kits combined with education (intervention arm n = 90). We estimated the effect of this 4-week intervention by comparing the groups post-intervention for change in KAP and diarrhoea infection. The average overall KAP score of the intervention group increased significantly from 8.54 ± 1.65 to 11.89 ± 1.60 (p < 0.001), between pre-intervention (t0) and 4 weeks after intervention (t2). In the control group, the change in average overall KAP score was not statistically significant (8.39 ± 1.72 to 8.74 ± 1.76 (p = 0.764)), between the t0 and t2 assessments. Diarrhoeal infection was reduced by 6% in the intervention compared to 2% in the control group. These findings support that a combination of short- and long-term strategies was more effective in reducing diarrhoea among tribal children than standalone approaches.