Mam, for changing surname a name change procedure need to be followed first you need to make an Affidavit with the maiden name added then same has to be published in 2 Newspapers.
Further after it is published in the newspaper, the copy of affidavit along with the Newspaper cuttings and consent letter of husband with requisite fees are to be sent to Controller of Gazette for gazette publication.
Kindly refer Complete Procedure laid down by department for name change of Minor:
http://deptpub.nic.in/forms/form060720168.pdf
You can seek help of advocate to complete the procedure.