On the child's Vivo phone:
- iManager (or Settings → Apps) → Autostart → Safe Lagoon On.
- iManager → High background power consumption / Backstage power → Safe Lagoon On.
- Battery → Normal mode, not power saving.
- Recents → Safe Lagoon → Lock.
Accessibility On. If menus are named differently on OriginOS, search Settings for "autostart" and "background".