This study aims to (1) estimate the prevalence of acute respiratory infection (ARI) symptoms, diarrhoea and fever in the previous two weeks among 3–4 year old children who are/are not at-risk of intellectual disability in 24 low- and middle-income countries and (2) to investigate possible inequities in access to treatment among affected children.Cross-sectional survey.Secondary analysis of Rounds 4 and 5 UNICEF Multiple Indicator Cluster Surveys (MICS) from 24 low- and middle-income countries (n = 99,934 children).Pooled estimates indicated that young children at-risk of intellectual disability in low-income countries were significantly more likely than their peers to have reported symptoms of ARI and diarrhoea in the previous 2 weeks, and significantly less likely to have received appropriate treatment. Pooled estimates indicated that in middle-income countries children at-risk of intellectual disability were significantly more likely than their peers to have reported symptoms of ARI, diarrhoea and fever during the previous 2 weeks. Symptomatic children at-risk of intellectual disability were significantly less likely than their peers to have received antibiotics/antimotility medication for diarrhoea or antibiotics for ARI symptoms, but significantly more likely to be prescribed anti-malarials for fever.These results indicate the existence of significant inequalities and possible inequities in the exposure to and the treatment of three major infectious diseases among children who are/are not considered at-risk of intellectual disabilities in low- and middle-income countries.