Hi Zubera,
Welcome to Apple Support Communities.
It sounds like you’re running into an issue creating an Apple ID for your son, iTunes is requesting payment information. Take a look at the article linked below, it’ll walk you through the process of creating an Apple ID for a child.
Family Sharing and Apple IDs for kids
Create an Apple ID for your child
Before you begin, make sure that you're using a credit card as your iTunes Store and App Store payment method. You'll use the security code on the credit card as part of providing your parental consent.
Use these steps to create an Apple ID and add the child to your family group:
- Go to Settings > iCloud > Family, and tap "Create an Apple ID for a child."
- Enter your child's birthday and tap Next.
- Review the Parent Privacy Disclosure and tap Agree.
- Enter the security code for your credit card and tap Next.
- Enter your child's name, tap Next, then create their Apple ID (username@icloud.com) and tap Next.
- Follow the onscreen instructions to set a password, choose security questions, and set up your child's account. Choose passwords and security questions that you both can remember.
After you add your child to your family group, they will have their own Apple ID that they can use on any Apple device. Your email address will be the rescue email address for your child’s account, and you can use it with the security questions you provided to reset a forgotten password.
I hope this helps.
-Jason