Objectives: This study aimed to estimate the prevalence of CDDs and ARIs and also to determine the factors associated with these conditions at the population level in Bangladesh.Setting: The study entailed an analysis of nationally representative cross-sectional secondary data from the most recent Bangladesh Demography and Health Survey (BDHS) data conducted in 2017–2018.Participants: A total of 7222 children < 5 years old for CDDs, and 7215 children aged below 5 years for ARIs during the survey from mothers aged between 15 to 49 years are the participants of this study.Results: The overall prevalence of CDD and ARI among children < 5 years old were found to be 4.91% and 3.03%, respectively. Younger children were more likely to develop both CDDs and ARIs compared to their older counterparts. Children belonging to households classified as poorest (aOR = 2.414, 95% CI (1.091 to 5.341)) and with unimproved floor materials (aOR = 1.821, 95% CI (1.145 to 2.896)) had a higher prevalence of diarrhea than those from households identified as richest and with improved floor material, respectively. Stunted children had 40.8% higher odds of diarrhea than normal children (aOR = 1.408, 95% CI (1.055 to 1.879)). Male children were 48.9% more likely to develop ARI than female children (aOR = 1.489, 95% CI (1.132 to 1.960)). Children of mothers aged below 20 years had 2 times higher odds of ARI compared to children of mothers aged 20 to 34 years (aOR = 2.166, 95% CI (1.403 to 3.344)). Children whose mothers had no formal education or had primary and secondary education had higher odds of ARI compared to children of mothers having higher education.Conclusion: Programs targeting children aged below 23 months should be designed and emphasis should be given to addressing barriers to mother’s education and household wealth to reduce CDDs and ARIs.