When three people play tag and two of them are brother and sister and the third is a kid they don't know well, the siblings usually go after each other again and again, and when the kid's mom asks them to politely stand to have their picture taken...
the sister who's It begins to plan use the situation to her advantage to tag her brother (never mind the kid standing next to her) - as you can observe from her brother's constant lean to his left....and as the pictures are being taken she strategically positions herself so as the last photo is taken she can reach out and slap him and joyfully cry: YOU'RE IT!
(If you enlarge the photo below, you will be able to see it clearly written on their faces. They both know their fate. Meanwhile, the one with dimples is blissfully unconcerned. His brothers are 5 and 10 years older than he. He knows how to lose over and over again like the back of his hand.)
And then he gets her right back and she comes inside crying to her mom that it's NOT FAIR!
That's usually how it goes, I think.