can it be a debit card for family share?

No, for legal reasons you will need a credit card to set up child accounts - from the page that you posted from :

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.

Well not everyone has credit cards. So because I don't have a credit card I can't monitor my child. That's a bit stupid.

You won't be able to set up a child account for them, the credit card is required for the above reason.