I have been reading the series of books by Gesell Institute of Human Development by Louise Bates Ames, Ph.D. and Frances L. Ilg, M.D. "Your One -Year- Old, Fun Loving and Fussy 18-24 month Old"; "Your Two-Year-Old, Terrible or Tender"; "Your Three-Year-Old, Friend or Enemy"; "Your Four Year Old, Wild and Wonderful"; "Your Five Year Old, Sunny and Serene"; "Your Six Year Old, Loving and Defiant". Even the tag lines are informative!
In the 1960's, Gesell pioneered the temperment research and arrived at the idea of a natural "biological maturation". A wonderful graphic and explanation here:
Gesell "emphasized that every child has a unique, inborn growth rate and temperament, and he urged us to respect each child's individuality. When, under the direction of the genes, the child's nervous system has grown to a certain point, the child will feel an inner urge to engage in each new activity...We help children the most by giving them opportunities to work on problems they find most interesting...When we push development forward- we shorten the time the child has to pursue her current interests." and natural growth is lost." Reclaiming Childhood, Letting Children Be Children in Our Achievement- Oriented Society", by Dr. William Crain, (Henry Holt and Co., New York, 2003).
Here in this link is a wonderful quick run down of the ages and stages covered in each of the books from the series. The institute has built upon Gesell's earliest work natural maturation equilibrium to disequilibrium by charting the growth as it moves between these two poles. "Smooth, Break-up, Sorting Out, Inwardizing, Expansion, "Neurotic" Fitting Together (Assimilation in nervous system).
As someone who likes to anticipate what I may encounter, I wish I had this road map to help me understand where on the journey I was. And for those of you with two children entering into the disequilibrium stages at the same time! I hope this helps you plan when to take extra care for yourself and for your child!