I'm the only person who builds MyBP Log, so this is short. The app doesn't collect anything. There's no server, no account, no analytics, no ads. Every reading you log stays in a file on your own phone, and the only way it ever leaves that phone is if you export it yourself.
Systolic, diastolic, pulse, an optional note, and a timestamp for each reading you log, plus your reminder schedule if you set one up. It's all saved to a plain JSON file in the app's private storage on your device (iOS's Application Support directory, if you're curious). None of it goes anywhere else unless you send it somewhere yourself.
If you turn on reminders in Settings, the app asks iOS for permission and schedules the notifications locally. That's handled entirely by iOS itself; nothing about your reminder schedule is sent anywhere. Turn it off any time in the app, or in iOS Settings under Notifications.
Since there's no server backing this app up for you, Settings has Export Backup and Restore from Backup buttons. Export writes a JSON file and hands it to iOS's own share sheet, so wherever it ends up (iCloud Drive, Files, AirDrop, whatever you pick) is up to you, and that destination's privacy practices are its own once the file leaves the share sheet. Restoring a backup just merges it in; you won't end up with duplicates if you restore the same file twice.
Delete a reading from the Log tab whenever you want. Delete the app and everything it stored goes with it. There's no copy sitting anywhere else.
This app isn't aimed at kids, and since it never collects anything off-device, there's nothing to hold onto or hand over for any user, child or otherwise.
If anything here changes, I'll update the date above and post the new version at this same address.
Something broken, or a feature you'd want? Email [email protected] and I'll get back to you.
A couple of things people usually ask about: if your readings disappeared after reinstalling, restore them from a backup file in Settings. If reminders aren't showing up, check they're turned on in the app's Settings tab and that iOS is actually allowed to notify you (iOS Settings → Notifications → MyBP Log). If you want something to hand your doctor, use the Report tab, pick a date range, and share it straight from there.