What sort of visa card is it, debit or credit ? To be able to set up a child account you have to have a credit card linked to your iTunes account due to privacy laws, debit cards are not accepted when creating child accounts : Family Sharing and Apple IDs for kids - Apple Support
Before you begin, make sure that you're using a credit card as your iTunes Store and App Store payment method. To comply with child online privacy protection laws, you will use the CVV or security code from a valid credit card 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 credit card before you can continue. After you create the child's Apple ID, you can change your payment method back to a debit card.