Antibiotic therapies currently recommended for the treatment of acute pyelonephritis (AP) in children, whether fully by the oral route or initially intravenous (IV, 3 days) followed by the oral route, have a duration of 7 to 14 days (10 days in France). In children with no prior urological malformation, the global clinical and microbiological cure rate after antibiotic treatment completion is around 95%. Recurrence occurs in less than 5% of cases in the 3 months following AP. Renal scarring, when documented, concerns 15% of children 6 months after treatment. Renal scarring can be associated with chronic renal disease. The investigators hypothesize that 3 days of IV treatment is equivalent to extending to 10 days with an oral to treat AP in children. The investigators also hypothesize that while achieving equivalent clinical and prevention of re-infections in the following 3 months, 3 days of IV treatment reduces the risk of acquisition of resistant strains of Enterobacteriaceae and increases the gut microbotia diversity compared to extending to 10 days with an oral therapy.