Separate adult private files from everyday family use, then check handoffs, account sharing and the copies outside the vault.
Identify the kind of sharing
A child borrowing a phone for a game, a family sharing one device, and several people sharing a cloud library are different situations. Decide who needs access to which content. A device passcode known to the family may also unlock some built-in private-album features.
Start with the ordinary surfaces: notifications, recent-app previews, downloads and the photo library. A private file imported into a vault may still have an original in one of those places.
Where NullVault fits
Separate pattern-addressed vaults compartmentalize app-managed content. Automatic lock helps close a session before the phone changes hands. Controlled import still requires a decision about originals and backups.
Do not make a child responsible for avoiding emergency or destructive controls. Test a harmless handoff yourself and check how the chosen app-pinning or guided-access mode exits on the actual device.
Choose the next task
Use when a child borrows your phone for a supervised handoff, showing one photo for a narrow viewing task, or shared cloud accounts for remote-library access. The family-phone guide provides detailed checks.
A vault is a file-storage boundary, not a parental-control system or a substitute for agreed family access rules.