Everyone subscribes to one link from their own app — Outlook, iPhone or Google. Nobody gets invited to anything, so nothing can be duplicated, and no one has to change platforms.

The link carries only approved events that aren't parents-only. A calendar app can't be asked for a PIN, so the link itself is the key — treat it like a password, and revoke it if it ever goes somewhere it shouldn't.

Events from a feed arrive parents only. Promote the ones the family needs; the rest stay off the kids' view. The board never writes back to Outlook.