Tom's answer is probably the easiest answer. But there may be an additional answer.
I know that pre-MagicBands you *could* set up a room charging account using a gift card. It wasn't the normal procedure, so a lot of CMs didn't know how to do it or had to refer to the manual at the front desk for instructions. What they would do is to set the charging limit equal to the balance of the gift card.
You can even set up a different source for each room charge account. But, you can only associate one source, so you can't do a gift card *and* a credit card.
Since the Bands link back to the resort account, presumably they will also refer to a charge account with a gift card as the source of funds.
But, you'd run into a problem if you're trying to complete a purchase that costs *more* than the balance of the gift card. Unlike just using the gift card at the point-of-sale where it would deduct whatever it could from the card and then require a second form of payment, the charge with the Band would simply get rejected because there wasn't enough funds left to cover the full cost.
So in a round-about way, we get back to just giving the daughters charging privileges on their Bands with your credit card, and then using the gift cards to pay-down the balance before checkout.
-Rob