Developmental theories are based on research that suggest philosophies about the children’s development. Theorists use the outcomes of their research to systematize and decode data grounded on a scheme to generate their theory. A theory is a methodical account of ideologies based on observed phenomena and their relationship to each other. A child development theory observes and interprets the children’s development and behavior. It identifies components in the children’s hereditary structure and the environmental situations that affect growth and behavior and the relationship of these elements. Numerous developmental theories provide information on ways to motivate, endure, guide, and nurture the children’s performance. Theorists established various developmental theories. Most theories differ and compete with each other, but they are frequently modified. This article describes some developmental theories and their theorists who have affected the disciplines of child development and early childhood education. Theorists include Jean Piaget, Lev S. Vygotsky, Burrhus Frederic Skinner, Urie Bronfenbrenner, and Sigmund Freud theorists. The article also discusses their theories, philosophies, and applications. Interpretations on the meaning of children’s development and behavior are explained for each theory. Though the theories are sorted into schools of thought, they are different within each school.