Abstract Background The Cholera Hospital-Based Intervention for 7 Days (CHoBI7) mobile health (mHealth) program was a cluster-randomized controlled trial of diarrhea patient households conducted in Dhaka, Bangladesh. Methods Patients were block-randomized to 3 arms: standard message on oral rehydration solution use; health facility delivery of CHoBI7 plus mHealth (no home visits); and health facility delivery of CHoBI7 plus 2 home visits and mHealth. The primary outcome was reported diarrhea in the past 2 weeks collected monthly for 12 months. The secondary outcomes were stunting, underweight, and wasting at a 12-month follow-up. Analysis was intention-to-treat. Results Between 4 December 2016 and 26 April 2018, 2626 participants in 769 households were randomly allocated to 3 arms: 849 participants to the standard message arm, 886 to mHealth with no home visits arm, and 891 to the mHealth with 2 home visits. Children <5 years had significantly lower 12-month diarrhea prevalence in both the mHealth with 2 home visits arm (prevalence ratio PR: 0.73 95% confidence interval {CI}, .61–.87) and the mHealth with no home visits arm (PR: 0.82 95% CI, .69–.97). Children <2 years were significantly less likely to be stunted in both the mHealth with 2 home visits arm (33% vs 45%; odds ratio OR: 0.55 95% CI, .31–.97) and the mHealth with no home visits arm (32% vs 45%; OR: 0.54 95% CI, .31–.96) compared with children in the standard message arm. Conclusions The CHoBI7 mHealth program lowered pediatric diarrhea and stunting among diarrhea patient households. Clinical Trials Registration NCT04008134. In this trial, young children in diarrhea patient households receiving the CHoBI7 mobile health program had less stunting and diarrhea compared with those only receiving the standard recommendation on oral rehydration solution for dehydration.