If You're Planning on Going to Disney World as Ariel

[Usagi]

Oh I guess I didn't respond when it arose, since it was started before I joined. Lol but yeah, if you look too much like the character, then little kids will want to take pictures with you and it's basically like stealing the real actor's job. Even for the Halloween Party, on the list of rules it says you are not allowed to pose for photographs or sign autographs if dress up as one of their characters.

[Miyu]

FYI, it's not just costumes that could be official Disney characters. Disney is pretty flip-floppy about their dress policy depending on which Land you're at, who's at the gate, what management is there, all that...but any clothing that could be construed as a costume tends to be a problem. I'm part of a Lolita fashion community, in which some of the members' everyday fashion generally consists of a modest dress with petticoat, mary janes or such, and some sort of headwear. There are several stories of people being turned away from Disneyland despite their outfits having no resemblance to any character, explanations that this is how they dress daily falling on deaf ears. I understand Disney's stance to a point (even if I don't like it), but I just wanted to point out that the limitation is not only when clothing resembles one of their characters.

Hey, that's where I learned about Disney's visitor dress policies! I guess, if you're a child, that anything "out-of-the-ordinary" or "fanciful" may make it look like you're a character. Specific character, maybe not, but think of all the fluffy-dress-wearing, head-eating-bow-donning, frilly background characters. You don't want a kid getting all excited and grabby while you're wearing Baby or AP, so although I love daily lolita fashion, I'd probably tone it down a bit, more subdued colors/prints/acessories, or just say the heck with it and do some daily fairy-kei.

At Disney, the "adult" costume seems to be after you're 10. And really, those are the only (Non-Disney) people I've ever seen wearing costumes in the park - little girls in princess dresses and boys dressed like Woody.

Not to say that you can't dress up - I have a few wonderful outfits that make me FEEL like a mermaid, and other mers will be able to look at me and think I'm a mer, but I'm not walling around in a tail and shell bra. You wanna be Tink? Wear the dress, do the makeup, try something a bit different with the hair, leave the wings. Easy - you'll be Tink-inspired, not Tink.
I'm working on a lolita/fairy-kei salopette made from vintage Little Mermaid bedsheets I found in great condition at a thrift shop. I'd feel just fine wearing that to Disney.

Yes, to us adults, the 15-year-old may look like a kid, but to children, there are two ages - kids and grown-ups. To little ones, even pre-teens, that 15-year-old and her boyfriend would be seen as adults by most kids, and their outfits were decent enough to make kids think that maybe they really were characters.