Set up a kid's device
Type the code from a parent
A parent gets it in Quilt under Settings → Family → Pair a device. It lasts 20 minutes and works once. After this, the calendar just opens.
Already paired in Safari but the home-screen icon still asks? Type a fresh code here in the icon once; each keeps its own pairing.
Are you the parent, holding the kid's device?
Sign in and set this device upYou'll be signed out again when it's done, so your account never stays on their device.