My son loaded a $50 iTunes card to his account, but songs purchased are coming off my family share credit card rather than gift card. He has an iPod touch 5th generation 32GB and I use an iMac.
iPod touch (5th generation)
This
Family purchases and payments - Apple Support
includes
Making purchases
After you set up your family, any time a family member initiates a new purchase it will be billed directly to your account, unless that family member has gift or store credit. First, their store credit will be used to pay the partial or total bill. The remainder will bill to the family organizer's card. As the family organizer, any receipts generated by the transaction will be sent to you.Learn more about how iTunes Store purchases are billed.
If you are doing that and the give balance is not being deducted then contact iTunes:
Music purchased not coming off son's loaded iTunes gift card, instead off my family share credit card.
