Background Intravenous fluid administration is one of the most common and important life-saving treatments in daily clinical settings, however it is not given as much attention as it should have. This study aims to evaluate the intravenous fluid’s use pattern in infants from birth until 18 months of age in Indonesia. Methods A post-hoc analysis of RV3-BB Phase IIb randomized, double-blinded, placebo-controlled trial was conducted in 1621 participants in Indonesia between January 2013 and July 2016. Any health events were documented in the trial as adverse events. Concomitant medication surveillance recorded all medications, including intravenous fluids (IVF) during the 18 months of follow-up. Information included intravenous fluid type, methods of administration, dosage, indication and duration. Results Of 1621 participants, 251 (15.48%) participants received at least one intravenous fluid for treating 294 adverse events during their 18-month follow-up period. A total of 333 intravenous fluid consumptions were recorded, 20 (6.0%) as fluid resuscitation, 273 (81.98%) as fluid maintenance, 40 (12.01%) as both maintenance and resuscitation. Isotonic fluids predominated resuscitation fluids (52 out of 60 [86.7%]) and maintenance fluids (166 out of 313 [53.0%]). Hyponatremia (1 case) was detected among those administered with hypotonic fluids (143 out 313 [45.7%] IVFs) for maintenance fluid. The most common indication for intravenous fluid was gastroenteritis (31.6%), with dehydration in most cases (65 [69.9%]). Modified WHO’s plan B diarrhea management was recorded in 22 [23.7%] diarrhea cases. Conclusions This study provides the information of intravenous fluid use pattern in 0–18 months children cohort in Indonesia. Some intravenous fluids were found to be unnecessary and not optimal, exposing the patients to the avoidable risks. These data justify the further study to evaluate intravenous fluid use in children and the needs of continuing training on intravenous fluid management among healthcare providers. Trial registration: Trial registration: ACTRN12612001282875, Registered: 12/12/2012, https://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?ACTRN=12612001282875