One of the most important principles of movement task training is the idea of task specificity which basically means that you learn what you practice.
This is because the the task demands determine the just right and specific stability, alignment and balance adaptations needed to support the sequence of movements that are needed to complete a task.
When an infant engages in intentional, goal directed actions they have the opportunity try different options for achieving a goal.
Will figuring out how to reach for a toy sitting on stable base with a little support around the hips
In this series of pictures you see Will (6 months) exploring options to maintain balance in sitting as he reaches for a desired toy.
His balance is still precarious and he topples sideways when he tries to reach to the side. To allow his to succeed I provide a small amount of support around the pelvis - task adaptation. This small amount of support provides a small amount of stability to the pelvis and allows William to experiment with moving the head and trunk relative to the pelvis.
This series of frames shows Will exploring different options for maintaining his balance when he reaches for a toy that is just out of reach. His actions are intentional and he has a goal - both important for successful learning.