There is absolutely no logically sound use case to mke a new emandate for MF in the name of minor.
Just invest in your MF , which ever tool you use, (For simplicity, you can use MF utility website or MFcentral website or the AMC website).
If you want to keep it separate for whatever personal reasons, you can create a new folio # and mke new investments in that folio #
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You can open a savings account for minor in HDFC or any bank.
HDFC has 5k min AMB called Super Children or something, just ask in any branch. You need to give your pan and Aadhaar and two photos of yourself and your kid. Don't take debit card, cheques if you don't need it.