Some experts says that the screens time is bad because the young see onlook at the screen for more than 8 hours per day.

For theyIt is very bad for them because ithey caused brain hurts headaches and eyes pain.

Too the blue light also makse them stay awake.

They do not sleep morefor more than 8 hours

Some experts says that the screens-time is bad because the young see on thetare at a screen more 8 hours a day.

For theyIt is very bad for them because they caused their brain hurt and eyes to hurt.

Too themuch blue light make them stay awake.

They do not sleep more than the required 8 hours

tThe sScreens

Since it is a title, it should be capitalised.

Some experts says that the screens isare bad because the young see onth look at the screen morefor more than 8 hours.

Since "screens" is plural, the auxiliary verb "is" should agree with the tense of the subject; therefore, it is not, it is "are". The Youth is more used than The Young. Look is more suited in this context, and add some extra prepositions and quantifiers.

For theym, it is very bad because they screens caused brain hurtdamage and eyes damage.

Since the pronoun representing the children (they) is the object, the pronoun should be changed to them, because them is the objective case, it is more suitable. The pronoun representing the screens is "they", but because this is a fresh sentence that has no mentions about screens yet, "they" should turn into "the screens". We are talking about abstract concepts here, so "hurt" should be "damage".

Too the blue light makes them stay awake too.

The "too" gets shifted to the end of the sentence. The blue light is one thing, so it should be "blue light makes' instead of "make".

They do not sleep more than 8 hours.

We are comparing here, so than is used. (Since it is showing a quantity not more than 8 hours)