The answer is B: clearly take a side.
A thesis statement is the main point or central message that writers include at the beginning of their writings since it explains the main ideas they are going to develop in the rest of the essay.
In every thesis statement not only does the writer include the topic of the essay but he/she also presents a comment or statement that tells the readers the writer’s position in relation to the topic being discussed; that is, if the writer is for or against the topic he/she is going to develop later.
In this thesis statement the writer has included the main idea that he/she is going to develop in the essay (that is, the effect too much television has on children), and he/she has also included the two opposite viewpoints regarding the topic. However, he/she has forgotten to include his/her opinion: Does he/she agree or not?
So, in order to improve this thesis, the writer must take a side.
In the body of the essay, the writer can include his/her reasons for being for or against the topic and he/she can even include quotes and statistics from different sources in order to support his/her ideas. They do not need to be included in the thesis statement.