I can't download any apps after using gift cards that now have no balance

The amount is in red because you still owe that money and the charge did go through but you did not have the funds to pay for it. There is no way to request a refund for a "Pending" charge because it has not been processed yet and you cannot cancel a pending charge as it has already been authorized by double clicking the side button followed by verification using FaceID/TouchID or Passcode.

Due to this your account has likely been disabled for any further App Store purchases. Being that you are a kid, you may need to be a part of a Family Plan where an adult can have a card on file. Here are a couple of Support Articles that relate to the situation you are in.

If a message says 'Your Media & Purchases account has been disabled' - Apple Support

If you can’t download or update apps on your iPhone or iPad - Apple Support

If a message says 'billing problem with previous purchase' or 'verification required' - Apple Support

Your device is still usable, you just won't be able to use the App Store, even for free apps, until the issue with your account has been resolved.

You may need a valid payment method on file to download apps – even "free" apps. You won't be charged for downloading "free" apps, but many "free" apps are full of "in-app purchases." Those cost real money, and you will be charged for them.

If you do not have a valid payment method on file, the App Store might not let you download any apps.

Sorry, I don't have that answer for you as Apple recommends to set up a Family Sharing plan and use Purchase Sharing where that credit card is added to your parents account, then gives you the permission to use it. That is the only recommended approach they have to allow purchases in the App Store from a kids account.

It may work as you described and deduct automatically by adding your parents card or you may have to tap on the red transaction you saw, then initiate the charge. The reason I can't specifically say it will work, is because Apple may also be looking to verify the information you have provided is actually correct and adding the card is usually how they do that, but in your case the information would not match as the account holder of the card is not you.

Also in the Support Article linked below titled "If you can't download or update apps...", step 2 says a payment method may be required. It is not the case for all, as you were able to download apps using only your Account Balance before, but if you get that message about requiring a valid payment method, then you may not have a choice.