It says something about how long I've had an eye on Japan that I'm not even curious about the dozen Yu-gi-ohs; I'm curious why there's an official-looking lady giving them a tour.
She has to lead them to the dueling arena
All of those are children in school uniforms, my bet is that they are on a school tour and either found somewhere to buy them or were handed out as souvenirs?
...Or the uniforms are just part of the Yu-gi-oh costume.
Notice the girl on the right with the headpiece in a female school uniform.
Maybe they are taking a trip and the teacher demanded that they all wear the same hat so noone gets lost. And the students were allowed to choose what to wear