Boy and Girl existed since the very beginning of time. As representations of the two basic genders. They were unassigned by the king of time and queen of space until the foundation of mankind. Do to karisma and charm Boy and Girl were finally assigned to be the world's coolest babysitters. They have shapeshifting abilities and they can shapeshift into whatever they want as long as it's not the opposite gender. So Boy can't look like a Girl and Girl can't look like a Boy.