Default Music app deleted from file system
You won't be able to restore 8.x anymore because apple isn't signing off on that version. You'll need to restore to the latest 9.3.2. Yes you will lose your jailbreak and erase your phone by doing that, but the backup should put your settings back.

Keep in mind since your phone was jail broken and in a questionable state due to your son messing with it, there is some chance that you'll end up with a bricked phone.