Thanks for the info, everyone. I would not recommend doing what I did: I found a "good deal" on 2 YOAMD Mickey Ears hats on eBay, and after shipping, I paid $17.67, which is $8.84 each. But I then took them to my local EmbroidMe store to have my kids' names put on them, and that cost me another $20! Highway robbery, but the first mom-and-pop embroidery shop I tried couldn't fit the hat into their machine.
I think I'd rather allow my kids to pick out their own hat, and enjoy getting the name put on it in the park. Maybe I'll still let them do it. Our plans for the YOAMD hats is to let "Tinkerbell" deliver them to the hotel room one night, as a surprise. They'll either fall in love with the YOAMD hats, and have the "I have one that you can't buy

, and I love it because Tink gave it to me" attitude, or they'll see the other options in the park stores and wish for one of those instead. We'll see.
But I know they'll be happy when they receive their presents from Tink, if only temporarily. I paid too much, but I'll look at it this way:
Two YOAMD Mickey Ears Hats on eBay: $17.67
Embroidery of names onto those hats: $20.00
Seeing kids believe in magical fairies: priceless!