If you would like to authorize someone as a guardian for your child, here is a sample template you can use to write an authorization letter as a guardian.
I am, [Name], the registered formal guardian of my [relation], [Child’s Name]. I am writing this letter to hereby authorize [Person’s Name] as the formal guardian on my behalf in conditions of unavailability. [He/She] shall observe all the duties of a guardian and act on situations as desired.
I request you to consider [his/her] actions of equivalent authority as of my own including signatures, etc. Also, [he/she] shall provide you with identity proofs for verification of their identity. Kindly take note of the same and cooperate for the stated concern. Also, feel free to contact me for further clarification at [Phone no.].