"You are a boy and I am a girl."
Translation:Tu es un garçon et je suis une fille.
Children use "tu" with each other regardless of their prior relationship, so assuming that the sentence really is one child talking to another, "vous êtes" wouldn't be correct.
I keep getting confused with 'et' and 'es' you should really make more games for this problem as im sure others gave difficulty
In the same way as in English we have "I AM", but "you ARE", in French we have "je suis" (I am) and "tu es" (you are).