We have all learned about our 5 senses: hearing, seeing, smelling, touching, and tasting.  What many of us are not taught (and I did not learn this until University!) is that there are 2 additional senses.  The propioceptive sense and the vestibular sense. Both senses are crucial to our ability to function day to day.  Propioception allows us to control our limbs without looking at them.  These receptors are located in our joints, muscles, and tendons. They send signals about their position in space to our brain.  For example, when driving, we can move our foot back and forth from break to the accelerator without looking and it allows us to type on the keyboard or play the piano without having to look at your fingers.

This is a good Brain Highway video that explains why children might crash, fall, or have trouble sitting still when they experience difficulties with processing propioceptive information:

Brain Highways: The Proprioceptive System