Through observation, Maria Montessori found a predictable schedule within child development when children had the most interest, focus, and ability to learn, and she called these times sensitive periods. Sensitive periods are windows of time in human development when children are at full readiness to learn, understand, and prioritize a new concept or skill. Many of the sensitive periods are linear and overlap with different areas of development. Sensitive periods are also a natural spontaneous phenomena in child development that cannot be forced, but observed for signs of readiness. Once you observe readiness, parents and caregivers can support a child with tools for them to lead themselves through their growth.
You can see here the overlap of infant and toddler hand development and equilibrium development. You can also see how not only there is overlap of sensitive periods, but how they can also shift. Math patterns to sensitive period for numbers.
The sensitive periods that are present at birth are:
Sensitive Period for Language (birth to 3 years)
Sensitive Period for Movement (birth to 4 years)
Sensitive Period for Refinement of Senses (birth to 5 years)
You can find examples of materials and tools that will help your child to develop and learn at their own speed. Here is an example from Monti Kids, but many of the tools are also pretty easy to DIY.
The full visual of child development and sensitive periods documented by Maria Montessori from birth to three years can be found here!