I thought Pirates and Princesses was bad enough, but this? OMFG! What next, Vicars and Tarts? Pimps and Ho's?
Like Piccadilly, the footballers and WAGs "culture" is definitely a British thing. They lionise sportsmen in America, but in a different way, if that makes sense. Sexualisation of children however - now that's increasingly common in both countries.
If it were just a "come as your favourite footballer," then that would still be tilted towards the boys, who are more likely to be encouraged to have an interest in football, but at least not be sexualised. Come as your favourite sports personality would be brilliant with all the wee Bradley Wiggins and Jessica Ennises, David Beckhams and Tanni Grey Thompsons running about! :)
But, this? I just can't imagine how to deal with this tactfully. Frankly, I'd not want to have anything to do with it, say DD won't be coming and explain why. But, that's hardly fair to her to not be able to join in with her friends. She could dress as a footballer, but quite likely would be teased by the other children for not conforming to the "gender dress code."
Even if she isn't teased, she'll see boys dressed in the role of skilled, well paid, high status sports personalities and girls dressed as sexualised, passive, shallow people who only have a purpose because of their relationship to those all important footballers. Okay, an 8 year old probably won't have that kind of deep understanding of the phenomenon, but she and all the other kids there will hardly be able to avoid the smash-you-round-the-head message of how boys are supposed to be and girls are supposed to be.
In a work related capacity, I was speaking with a psychosexual therapist today who sadly confirmed how exposure to these and other sexualised messages in childhood have a very negative impact on the sense of self, on behaviour and the capacity to form relationships. Interestingly, she said the most crucial age seems to be about 8 :(