We are going in about a week! DD, DNephew (8) & DNeice (13) are all heading to BBB and can't wait.
I wouldn't worry about the heat, we aren't. Who says that they MUST wear a costume? I've seen BBB princesses in a tank top and shorts, sporting the nails/hair/makeup & sash. Yeah, they might not get the same drastic reactions from strangers, but I'd put my kid in a t-shirt before I'd skip it.
Have fun and I hope to post pics when we return!