My guess is that most young kids are bored sick at the meetings. The light relief for them comes however, when their parents prod them in the ribs and give them an answer. These usually consist of the Jehovah, Jesus, etc. type answers.
But sometimes it appears that kids are used to answer the sort of questions that are simply an insult to an adults intelligence. For example, the question may be asked, what is Gods greatest quality? Now, we all know the one word answer. To a thinking Christian, there may be a lot that could be said in reply, perhaps something that is quite challenging regarding Gods love. However, in the average question and answer session, it is the one word answer that is required, then the conductor can quickly move on.
Kids are also used to answer the trickier doctrinal questions, such one from this weeks book study When and in what way did Babylon the Great undergo a fall? In this case it is easier to use the kids, their answers can be taken as fact, rather than have an adult try to present facts and reasons behind the stated answer.
The worst cases though are kids being used to answer during those discussions of taboo subjects, where the adults are too embarrassed. I have certainly heard youngsters answer on topics such as martial dues, etc.
Eyeslice