Anecdote, I started fidgeting by varying eye focus and depth - can't get forced to sit still if your fidgeting is barely perceptible - at a very young age and have the best range of accomodation of anyone I know. Can also easily perceive chromatic aberration/my eyes needing a different focus setting for different wavelengths.

I'd love to know if some sort of focus training exercises for eyes starting as children would help everyone.