Background: Young children are at high risk of urinary tract infections (UTI) that present as asymptomatic non-specific signs without clinical presentation. UTIs put children at risk of malnutrition, and thus early diagnosis, nutritional management, and medication are important. The administration of oral nutritional supplements (ONS) with an energy intake of 400 kcal/day is thought to be an effective strategy to provide balanced nutritional needs. Objectives: This study aims to investigate the clinical symptoms and growth pattern of young children with UTIs and with clinical symptoms of poor feeding and growth faltering who received medical treatment and nutritional intervention for three months. Methods: A cross-sectional analytical study was conducted from January 2019 to December 2020 at the outpatient installation unit of Husada Utama Hospital. Subjects were children aged one to five years old, with the main complaint of poor feeding and constant weight gain. UTIs were identified according to the urine culture results. If the count exceeded 100.000 cfu/ml, it was determined as a urinary tract infection. Results: A total of 37 children were enrolled in this study and received diet advice, ONS, and medication. The proportion of boys was higher than girls in this study (21 to 16, respectively). Undernutrition was experienced by 14 subjects (37.84%) who were stunted or severely stunted (13 subjects or 35.14%), underweight or severely underweight (seven subjects or 18.92%), and wasted (four or 10.81%). It was shown that ONS improves mean corpuscular volume (MCV) and mean corpuscular haemoglobin (MCH) significantly, and slightly increased haemoglobin though there was no significant difference. White blood cell (WBC) and lymphocyte levels reduced after ONS intervention. Conclusion: Nutritional intervention with ONS improves erythropoiesis (MCV and MCH) but reduces WBC and lymphocytes in children with UTIs.