Maria Montessori being an educator observed that the physical developments in each child, like crawling, walking, talking, etc happen during the same years. It is easily detectable in a child, but observing the mental development milestones is a little difficult. It hence has divided this into four important stages called the absorbent mind, reasoning mind, social consciousness, and transition into adulthood.
Young minds from birth to six years old are sensitive and it is important for parents or adults to support them at this stage.
The Montessori theory of child development is called the four distinct planes of development that is an important phase between infancy and early adulthood. These developmental phases include both physical and psychological changes and accordingly the education system needs to be planned wherein children get the maximum benefit of learning.