how to make gift card shared in family account

what do I do if the gift card has already been added to my sons account?

Caelan,

If it has been redeemed to your son's account, the credit can be used by your son for purchases, which can then be shared among the Family Sharing group.

Kuejin,

If you want to use it for their purchases, you have to redeem it to their account, not yours. That way they will have a store credit and it will be used to pay for their purchases.

See this document:

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.

KUejin,

THis information would be helpful if it was written on the iTunes gift card but unfortunately it isn't.

what do I do if the gift card has already been added to my sons account?