Unused balance on a Disney Gift Card CANNOT be refunded as cash.
Unused balance on a Disney Gift Card NEVER EXPIRES, so you can simply save the leftover for your next trip (that's what I do).
But if you never plan on going to WDW again, ever, and really, really, want that leftover $4.28 or whatever you have on the Gift Cards refunded as cash, then a little prior planning can work for you - do this:
When you check into your Disney resort, hand over the kids Gift Cards and have the check-in CM enable room charging on the kids' key cards. The Gift Cards will be a deposit, and the kids' charging limit will be whatever you set, up to $500 if you stay in a Value resort, up to $1000 if you stay at a Moderate, and up to $1500 if you stay at a Deluxe.
When you put down cash, Disney Dollars, or Disney Gift Cards as a deposit to enable room charging, any remaining unspent balance is refunded to you in cash when you check out of the resort. The only drawback to this is minor - you cannot use the express checkout feature, because you have to go to the front desk to get the refund. However, it does have a positive side effect - you can get a print out, at any time, of exactly what was spent, and where, and when, for each of your key cards. And if the key card is lost, it's a lot easier to replace while at WDW than a Disney Gift Card.
Instead of purchasing a Disney gift card, you can go to your local
Disney Store and purchase Disney Dollars. Any unused Disney Dollars can be traded in for cash at Guest Services at the end of your stay.
Enjoy your stay!
That's limited to $100.