This is the guide that would have saved me an afternoon. In order, with nothing padded out.
Gather the documents
Your child's birth certificate, your PAN, your Aadhaar, and your bank account number and IFSC. Keep proof of your relationship to the child handy — some fund houses ask for it.
Check whether your KYC is done
If you've invested in a mutual fund before, it probably is. You can check on the KRA websites. If it isn't, doing it online takes about fifteen minutes — PAN, Aadhaar, a selfie, done.
Choose where to do it
Directly with an AMC, or through a distributor platform. Going direct means a separate login for every fund house. A platform gives you one place for all of them. Nuberry, Kuvera and Groww all do this.
Open the minor folio
Select the minor option, enter your child's name and date of birth, confirm your relationship as guardian, and link the bank account the SIP will run from.
Pick a fund and start the SIP
Choose your monthly amount and SIP date, then confirm the bank mandate. After that it runs on its own every month.
Set it up once. Let it run. Check in once a year. That's the whole job.
Markets will go up and down, and that's normal. The one thing worth knowing in advance: stopping the SIP during a fall is the most common mistake, and it's the point at which the same money buys the most units.