A mascot costume. The must-have item for any kidnapper...
Nobody can see who you are, it's hard to notice if there's an extra mascot walking around and the children flock to you even without offering them candy =P
Did they put on animal mascot costumes because they were paid to do so by the Ueno Park Zoo or are we going to be left in the dark as to what they were planning because the Colors sensibly didn't want to follow adults wearing disguises who suspiciously wanted the girls to follow them?
@kleiner I believe you're supposed to use a direct link when embedding pictures (i.e. https://i.imgur.com/9nFrFJK.png instead of https://imgur.com/9nFrFJK), like so: