On the child's OPPO / ColorOS phone:
- Settings → App management → Safe Lagoon → Allow auto startup.
- Allow Background running / disable background freeze for Safe Lagoon.
- If there is a Security / Phone Manager app: Privacy permissions → Startup manager → allow Safe Lagoon.
- Settings → Battery → turn off Smart power saving / high background power limits for Safe Lagoon.
- Recents → Safe Lagoon → Lock.
Accessibility: Settings → Accessibility → Safe Lagoon → On. Battery: Unrestricted if the menu exists.
Older R9 / R11 menus are gone; if you still have one, uncheck every battery restriction listed under Safe Lagoon.