The child will need an AppleID and password
The child's AppleID will need two-factor authentication disabled
The child's phone will need iCloud backup turned on and current
How does it work?
To retrieve the new data from your child’s device, the phone must complete an iCloud backup.
Apple does an automatic iCloud backup every night and you should have access to new data once a day.
This requires that the iCloud Backup setting be turned on so that at night the device is idle, charging and connected to WiFi, which is when the Apple iCloud back up will complete.
The device must be idle during the nightly iCloud backup or it will not backup the device.