Keep frequently eye blink can help keep eyes moist. It is good to eyes. But if your children keep blink too much, it is not normal. And commonly, constantly eye blinking is caused by eye irritation from bright light, dust, smoke, or a foreign body in the eye. Besides, Allergies, infections, and dry eye may also increase the rate of blinking. According to your description, your kind's eye blinks maybe caused by the bright light since the he was watching TV.
It is not a big deal that your kid' eyes keep blinking while watching TV. While your kid was watching TV, his or her eyes were stimulated by television image because as the television screen flicker and the pace of change, which will lead to vision of children with central hyperexcitability. Please warn your kid not to keep watching TV for a long time, and also keep a distance from the screen. At the same time, you had better to help your kid to relieve stress.