Kindly keep following documents ready to avoid last minute problem..
List of documents you need to keep ready :
1) Immunization card
2 Medical fitness certificate from your pediatrician(some schools ask)
3) Affidavit in case of Single Parents.
4) In case of sibling, the school Identity Card of sibling studying the school or marksheet etc
5) Adhaar card of child and parents ( if you dont have, apply immediately bcoz few schools ask for it)
6)Passport Size Photographs of the Child as well as the parents.
7) Alumni Cases - Proof of Alumni
8) Address proof ( Bank statement, BSNL bill, Electricity bill).. in case of Tenant (Rent Agreement)
etc
9)Birth Certificate