Fascioliasis is reported in five Vietnamese children aged 4 years or younger. A 10-month-old girl child and a 12-month-old boy child are the youngest patients ever diagnosed. Eggs in stools suggested an infection occurred at 5-6 months and 7-8 months of age, respectively. DNA sequencing and egg size indicated this to be the first report of a verified Fasciola gigantica infection in so small children. No specific diagnosis could be obtained in two 3-year-old children detected in the acute phase. A big and gravid ectopic F. gigantica-like worm was surgically found in a 4-year-old boy presenting with peritonitis. A worldwide review showed only 38 past cases in preschool children. They included 3, 7, 12, and 16 cases of 1, 2, 3, and 4 years, respectively, with a faster infection increase in males from 2 years onward. Reports were from all continents, except Oceania, including severe complications and death. The causal agent, when specifically diagnosed, was always Fasciola hepatica. Analyses include detection in hospital, surveys, and family outbreaks; infection sources; disease phases; parasite burden; ectopic cases; symptom onset; eosinophilia; biochemical markers; and clinical complications. C-reactive protein, creatinine, and γ-glutamyl transferase are the most useful biomarkers. A serological test and a coprological analysis are recommended for so small children, in which typical symptoms may be overlooked. Treatment problems were described with many drugs, except triclabendazole. Triclabendazole should be considered the drug of choice for such small children. The possibility of a very early infection by Fasciola spp. should be henceforth considered.