There has been additional evidence that the more time children spend outside the better chance they have to stay out of glasses.  Majority of school age children need to wear glasses to correct nearsightedness or myopia.  Myopia gets worse during the teenage growth spurt.  It is imperative for elementary school children to have at least an hour of outdoor playtime.  A review of scientific literature found a significant protective association between increasing time
spent outdoors and prevalent myopia in nearly 10 000 children and
adolescents aged ≤20 years.  Each increase in hours per week of time
spent outdoors was associated with a 2% reduced odds of myopia (nearsightedness).  An increase in 7 hours of time spent outdoors per week (1
hr/d) equates to less nearsightedness.

 There are a myriad of possible mechanisms by which spending time
outdoors may protect against the development and progression of myopia (nearsightedness).
They include increased release of retinal dopamine in response to
sunlight (dopamine inhibits axial elongation in experimental myopia,and the protective effect can be blocked by the dopamine antagonist spiperone), increased light intensity outdoors
(leading to pupil constriction, increasing depth of focus, decreasing
blur, and slowing of eye growth), and the low accommodative demand (focusing) for
distance vision. 

Bright light has been shown to be protective of myopia in animal experiments using ultraviolet-free light.  Based on that evidence, one might support an old myth not to read in poorly lit rooms.  More focusing power is required to read in poorly lit rooms and it is the focusing muscle (ciliary body) if placed in overdrive will lead to development of nearsightedness.

Because there is no protective association between indoor sports and myopia,
unlike outdoor sports, it suggests that physical activity may be a
surrogate for outdoor activity. This is supported by a cohort study with
2 years of follow-up in 156 university students where physical activity
time was higher in nonmyopes and associated with hyperopic refraction
(0.175 D per hour of physical activity per day; P = 0.015) after
adjustment for potential confounders, although there were no differences
in objectively measured physical fitness levels between myopes and
nonmyopes (P = 0.321).

Get your kids outside and take advantage of the great summer weather!  Just don’t forget the sunglasses!