As others have said, you’re not loading money or a credit card on a magic band. By using a magic band, you’re simply charging to your room (which has a credit card on file).
I would also go with gift cards, rather than trying to put more than one credit card on a room. I tried that with a friend several years ago, and all of our charges kept going to my friend’s card since the room was in her name. We did each have separate credit cards with separate PINs linked to our individual magic bands, but my charges kept going to my friend’s credit card. After multiple trips to the front desk to straighten this out, I gave up trying to charge using my magic band and switched to cash/credit card. It was a huge hassle!
That was several years ago, and maybe they’ve improved things, but I wouldn’t count on it. I’d go with gift cards for each kid, and no charging to the room.