Erector Spinae Plane Block Versus Caudal Epidural Analgesia

The goal of this clinical trial is to compare the analgesic effect and safety of erector spinae plane block vs caudal epidural block in paediatric population undergoing lower limb cancer surgery. The main questions it aims to answer are: * Which of them has a superior analgesic effect. * which of them is more safe and has less complication rate. Participants or their guardians should agree to share in the study (after full explanation of risks and benefits) to receive one of the previously mentioned regional blocks in conjunction with the classic balanced general anaesthesia.