how to remove apple pay from a child's iphone

Hi Michael Beck2,

You can choose to add or remove cards from Apple Pay using the tips below:

• Change or remove the payment cards that you use with Apple Pay - Apple Support

"Remove a card from Apple Wallet

You can remove a debit or credit card from your device.

How to remove a payment card on your iPhone or iPad

1. In the Wallet app, tap the card that you want to remove.
2. Tap the More button .
3. Scroll down and tap Remove This Card.

How to remove a payment card on your Apple Watch

1. On your Apple Watch, tap the Wallet app.
2. Tap the card that you want to remove.
3. Scroll down and tap Remove.

How to remove a payment card on your Mac with Touch ID

1. Go to System Preferences > Wallet & Apple Pay.
2. Click the card that you want to remove.
3. Click the Remove button ."

Regarding the app itself, you can restrict the Wallet app under Settings > Screen Time > Content & Privacy Restrictions > Allowed Apps.

Finally, the best option may be to use parental controls on their device. See options for configuring those here: Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support

Take care.