How to share with a family member or other
Starting with iOS 13.4, iCloud Drive supports sharing folders with people that you invite. This enables you to share your data with another person.
1. Store your file on iCloud Drive
You must be storing your data as files on iCloud Drive, as explained here.
2. Share your Folder with the other person
Share the iCloud Drive containing your file(s) with the other person. How to do so is explained by Apple here.
3. Open the file on the other person’s device
Instructions for the other person: Open the app, then tap on the folder button at the top. Locate the file in the folder that was shared with you. The child’s data is now listed in the app and you can open it to edit measurements, which will be synced to other users and devices via the iCloud Drive file.
Why this is not available for free
Free users are limited to one child. If file access was available for free then anyone could use files to track multiple children without purchasing the upgrade. The good news, however, is that Growth+ supports Family Sharing, so you do not have to buy it more than once if you use Family Sharing.