Rousseau felt that although children began life without any knowledge, Nature endowed each child with a particular way of thinking and feeling.
Nature is like a hidden tutor who prompts the child to develop different capacities at different stages of growth.
Rousseau sets out four developmental stages, what a child was capable of acquiring during each one and how. They're reminiscent of Piaget's or Erikson's stages (they are traditionally the ones I think of as developmental psychologists). Both Locke and Rousseau offered their theories of educating children to become "successful" adults. Locke seeing this success defined by the adult's ability to control individual desires - to seek the approval of society so that one might serve it. Whereas Rousseau saw people as driven by primitive urges, fighting being crushed by society. He felt that a successful education permitted the adult to develop independent ideas and morals so as to stand up to society rather than conform to it. We're still playing out this debate today. If any of you are fans of Lost, you will recognize it as one of the themes of the show, hence a character named John Locke.