The goal of this clinical trial is to learn if dupilumab works to treat severe nephrotic syndrome in children. It will also learn about the safety of dupilumab. The main questions it aims to answer are: * Does dupilumab reduce the time to relapse of nephrotic syndrome? * What medical problems do participants have when taking dupilumab? Researchers will compare dupilumab to a placebo (a look-alike substance that contains no drug) to see if dupilumab works to treat severe nephrotic syndrome. Participants will: * Receive an injection of dupilumab or placebo (just under the skin) every 2 weeks (if ≥30kg) or every 4 weeks (if \<30kg) for 24 weeks (6 months) * Wean down their prednisolone dose after starting the injections of dupilumab or placebo * Visit the clinic once every 2 weeks for checkups and tests * Keep a nephrotic diary to record down the urine dipstick result each day, together with the dose of prednisolone taken If protein returns in participant's urine, they will have completed the study at that point. However, if the participant is found to have received the placebo, they will be offered to receive dupilumab for up to 24 weeks.