kid‘s eyes

The eyes are the window to the soul, the kid's eyes are symbols to of pure purity and innocent,  However,  It causes have shortsight of the students who have too much homework or often play too much many computer games could develop poor eyesight .  So schools has have already carried out the eye exerises ,and encouraged students to play outside, seeing green plants and enjoying nature.

I learned the expression  as "The eyes are the windows of  the soul," but it'sOK to use to also.
Purity is the noun and pure is the adjective.
In the next sentence, your use of it causes...is using Chinese grammar.  We could write this sentence in different ways in English.  For example;

Too much homework can cause poor eyesight.  (sth can cause sth)
Doing too much homework can cause... (verb + object can cause)
Poor eyesight can be caused by too much homework. (sth can be caused by sth)

The medical term for shortsightedness is myopia.  In everyday language we usually say a person is near-sighted,( not shortsighted.) or myopic.
We use many and not much with computer games because game is a count noun.
Schools is plural because you are probably referring to more than one school.

Here is how I would write it in everyday American English.

The eyes are the windows of the soul.  A child's eyes are symbols of truth and innocence.  However, doing too  much homework and playing too many computer games could damage the eyes and cause myopia.  Schools have already instituted programs of eye exercises, encouraging students to play outside, look ar green plants and enjoy nature.

Kid is slang and child would be preferable here.
Institute in this sentence means to initiate or to begin.   A program is first initiated and then carried out.

There are two things that influence English grammar, time and number.  Whenever we speak we are always conscious of two things, exactly when something happened, and how many are involved.  The proper tense and number (singular/plural) are not absolutely necessary for understanding but are absolutely necessary for proper English.