The goal of this clinical trial is to use modified Brentuximab Vedotin+doxorubicin+vinblastine+dacarbazine+Rituximab(BV-AVD-R) regimen in Chinese Classical Hodgkin's Lymphoma(HL) children. The main questions it aims to answer are:
* \[Overall Response Rate(ORR) :Complete Response(CR)+Partial Response(PR)\]
* \[progression-free survival (PFS), event-free survival (EFS) and overall survival (OS) at 6 months and 1 year.\] Participants will be given modified BV-AVD-R regimen according to rapid early responders (RER) or slow early responders (SER) after 2 cycles.