Q: Why do you need a credit card for adding children to family share, don't have a credit card or want one.

For info you are talking to fellow users on these forums, not iTunes Support nor Apple.

Credit card details are required for child accounts due to child online protection laws : Family Sharing and Apple ID for your child - Apple Support

Before you begin, make sure that you're using a credit card or UnionPay as your iTunes Store and App Store payment method. To comply with child online privacy protection laws, you will use the CVV, verification code sent via SMS, or security code from a valid payment method as part of providing your parental consent. If the card on file is a debit card or another payment method, you’ll be asked to provide a valid payment method before you can continue. After you create the child's Apple ID, you can change your payment method.