Watching TV will not harm your eyes or vision if the TV room is lit properly & if you follow a few viewing tips. But watching for long stretches of time can leave your eyes fatigued

Eye Care For Computer Users

Few Tips
Normally lit room
Avoid viewing in a dark room.
Adopt the set's brightness & contrast to room lighting
Keep proper distance- It is best to watch TV from a distance of at least five times the width of the picture.
Have the set at approximately eye level. Avoid having to look up or down at the picture.
Avoid staring at the screen for lengthy periods. briefly look away from the picture around the room or out the window
Wear lenses prescribed for vision correction if advised to do so by your eye care practitioner.

Consult your eye care practitioner if

Your child persists in watching TV from a short distance
You get watering while watching TV.