Face ID

Setting up the child’s device under your AppleID is strongly NOT recommended.

While admittedly an expedient; setting up the child “later” becomes exponentially more difficult as time advances.

Recommend you make a relatively minor investment in setup time now; you’ll thank yourself later.

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If the iPad is meant for the child’s use, would recommend that you (presumably the family organizer) FIRST create the child’s AppleID as described here:

Set up Family Sharing - Apple Support

Create an Apple ID for your child - Apple Support

THEN

setup the iPad w/ the child’s AppleID

THEN

Apply Parental Controls

Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

You can do it as a later step. How to set up and use Face ID is described in this support article --> Use Face ID on your iPhone or iPad Pro - Apple Support

- including how to turn on