How to change my child age Restrict

On your iPhone, iPad, or iPod touch

1. Go to Settings > [your name].
2. Tap Name, Phone Numbers, Email. You might need to enter your Apple ID password.
3. Tap Change Birthday or Birthday.
4. Update your birth date, then tap Done. If you're changing a birth date for a child, learn what to do.

Update the birth date associated with your Apple ID - Apple ...

If you created an Apple ID for your child, the age cannot be changed. From this support document, Create an Apple ID for your child - Apple Support

Be sure to enter the correct birth date — you can't change it later.

Nice find !! 👍

Explains a lot of “teeth gnashing” in previous threads from folks attempting to do so.