Hi
josang0817,
You mentioned that this came from an online lecture ... what's the source of that lecture?
To be honest, this does not look like high-quality material. I don't agree with their answers. (I have a perfect score on Verbal and five years' experience coaching.)
Do we want to describe something that is true
at the moment of watching TV?
If so, -ing
Do we want to describe something that is true
all the time about a particular group of children who watch TV in general/regularly?
If so, "who watch".
Here, "who watch TV" is a
defining relative clause -> it specifies, of all the children in the world, which children we are talking about. "Watch" is the simple present, so it describes an activity that happens regularly. ("Children who watch TV" do it regularly).
*If by chance you are based in India, be careful on this, as Indian speakers of English may use the present progressive to describe a regular/repeated action, but this is not correct in American English. ("Children who are watching TV" implies "Children who are in the middle of watching TV" in American English, although speakers of Indian English might use it to refer to children who generally/often watch TV.) In American English, and thus the GMAT, if an event happens regularly or if a fact is true all the time, use the simple present.
So, #2 is definitely not "watching", and should be "who watch"-> this is a general statement about a certain group of children and their overall awareness. (The kids' awareness of world events doesn't disappear the moment they stop watching TV.) We don't want to say that they are aware of world events only at the moment of watching. For #1, I could accept either "who watch" or "watching" -> it could be true at the moment of watching TV, or in general.
But again, these aren't great sentences. A better use of "watching" would be something that is clearly about the same time: "Studies show that children watching TV are slower to respond to parental commands than children playing with wooden trains."
Here, the idea of "in the middle of" doing something is clear.
Does this help?
Best, Jenn