@VinaySuri Sir I'm just a customer of bank similar like you hence I might not abled to clarify your concerns.
However after reading so many concerns over CG forum I visited branch to understand further since I'm also maintaining a minors account for my kid with HDFC bank, They informed there can be several reasons for debit freeze in minors account (eg. KYC not in line with transaction performed , frequent debit/credit, large amount debit/credit, debit/credit to/from online gambling sites, more transaction on minors account compared to major account etc. etc.) so many reasons explained. The purpose of minors saving account is to create wealth for children as they grow up and teach them how to manage money with limited excess available to children.
These short of conversation had with HDFC branch officials with regard to minors account ongoing concerns.