There's a similar thread going on, but since there are no replies here yet, I'll comment.
The best thing to do is put your CC on the room, and allow charging privileges to both of the kids. Monitor their spending, via receipts. Then, once they've spent the amounts of their gift cards, go to the front desk of your hotel and use the gift cards to pay down the running invoice.
This way, if you have a $25 gift card, and they buy something that's $25.05, it won't reject it at the register.
Be sure to pay down the balance before the last night of the trip, so that it doesn't reconcile and charge your card before you have a chance. Do it as soon after they've hit the gift card amounts as possible, especially if you're charging lots to the room.
I honestly can't answer your original question about multiple cards on one room. I don't think that's possible, but it could be.