I was just in NYC and saw Billy Elliot... which is absolutely fabulous by the way... and that's an understatement!! The top picture is definatly the Broadway cast with Kiril Kulish. I have to agree with Katherine... the boy in the bottom picture is not one of the three boys that is currently playing the role of Billy on Broadway... which would mean that is probably a photo from the London production... although the girl does resemble Casey Wyland a bit.
Below is a link of an adoreable video taken by Gregory Jbara, who plays Billy's dad in the show. It is an interview of the 11 ballet girls (including Erin and Casey Wyland) in their dressing room after a rehersal. Too cute!