First, and perhaps most importantly, there is Piagetian theory. It proposes that the child develops through five different stages, starting with the sensori-motor stage and ending with moral awareness. Then there is Freudian theory. This proposed five stages also, but based on his theory of the unconscious, these stages represent gratification of needs: beginning with the oral stage, sucking, and ending with the genital stage and forming of adult relationships.
Third is Erikson who refined Freudian theory into eight stages, relating this to what conflict was relevant to each stage. Fourth is Gesell, easier to understand and useful in clearly outlining developmental skills and the average age that these might be achieved, such as climbing stairs one foot after the other. Lastly, and least importantly, is Bronfenbrenner who studied children in light of social changes and put their development into the context of community.