#Due to the limit of characters, I will continue here.

*1 The subject of "Let's" includes readers of this article. Because this statement is made by you, it is politer to say "Let me".
*2 "books" talked here is not modified,　they are just general ones, so I think it's better "the" before books here be omited.
*3 Putting this phrase here, the meaning of this sentence gets clearer.
*4 Please note that "listen" is an intransitive verb and needs some prepositions.
*5 Usually the subject of "have to" phrase is people.
*6 If there isn't special need, I think it's better to describe with plural form. Because many of families may have several TVs or radios.
*7 Or you can say "still getting larger and larger".
*8 Better to use words described in question.
*9 If you put "the" before people here, readers may think this word "people" is modified, or this "people" is some kinds of the people you have already talked. I think it's better be omited.
*10 It's better to use these verbs having passive meaning, corresponding to precedent "see" of television.
*11 Pleae don't forget that your task here is to figure out "the most effective" media :)
*12 The usage of "respectively" is not usual. Or you can say "Parents and children watch news and cartoons respectively."
*13 Pleaes note that the subject here is not "we". The sentence can be changed like this way: "To access information gets easier for us".
*14 This is very clear even if it isn't described.

Hello Claire, I listed the points I noticed in this statement.
Please feel free to ask me if anything not clear.
Hope this helps!

I think that the most effective way to get information is by television for the following reasons. Let's me*1 compare some features of books, radio, and television. 

First(ly), for (the)*2 books, people have to be self-motivated for acquiring information*3 to buy and read (the) books (for acquiring the information). On the other hand, listening to*4 the radio and watching television don't really have to*5need being self-motivated. You can just sit on a chair or a sofa and receive thosesuch information from the devices. From thisthese points of view, people would tend to use radio and television to get (the) information because of thetheir convenience and the effectiveness. There is also a point to support this that, people get lazier than before.
Secondly, the cost of listening to the radio and watching TV areis cheaper than reading books in the long run. Therefore, the proportion of the people having (a) TVs or (a) radios*6 at home is larger than before and still tends to get larger (and larger)*7. Having (a) televisions andor (a) radios is not a hard task(or: special thing) anymore.
Thirdly, TV programs could be more creative than the other two types of communication medias(/ways)*8 because we can see (the)*9 people and scenes on the screen. For example, my mom loves watching soaps everyday on TV. But can we see those soaps fromon books or the radio? Definitely no. We can only see(/read)*10 words fromon books and hear(/listen)*10 the voices of DJs from the radio. All in all, television is more attractive*11 to us.
People are used to watch television everyday now. Parents watch news and children watch cartoons respectively*12. Since we are*13it gets easier for us to access information than before*14, we should have the ability to judge whether the information is correct or not.

aaa: correction, aaa: suggestion, aaa(/bbb): aaa is better, ( ... ): can be omited