Congrats on your "little souvinier" (I know he/she wasn't created there, but I love that commercial!)!
I like the ears idea, and I am sure you have an idea what you are going to teach the kids to call them, so there shouldn't be any strife or family ******* over it I wouldn't think...
There might also be shirts there to get like, "Best Grandma ever" or something..
I think getting a picture of the two of you in front of the castle with a crazy shirt on you with an arrow pointing to your belly might be fun too! Ok tacky maybe, but fun!