First:
aliza249 wrote:
his iphone XS (same my Apple ID)
This is a huge mistake that should be fixed immediately. Each person, regardless of age, requires her/his own, unique Apple ID.
Create an Apple ID for your child - Apple Support
Be certain his iPhone XS is thoroughly cleansed before he “moves in” using his new Apple ID.
What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support
Then:
Help your child set up an iPhone, iPad, or iPod touch - Apple Support
Use Family Sharing to provide parental consent for your child's existing Apple ID - Apple Support
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Now regarding Notes, open your Notes app, tap “<Folders” in the upper left, and see if you find a “Recently Deleted” folder.