I totally disagree with children working at early ages of their lives. Its fundamentally wrong to get work done from kids and pay them while it's their age for playing and going to school. My argument is based on the below reasons and examples.
In country like India, where I belong, I have seen people employing children doing all sorts adults work. And the work these kids do is no less than what grown ups. Even though working almost same, they are paid much less. These children do all sort of labor work, working in factories and dangerous environments at such a young age. Even if they wish to study, either because of lack of resources because of poverty or inadequate facilities for schooling they don't get change to get education and are made to work so as to be another earning member in the family. Even people do not feel ashamed employing children of such young age. I don't think the learn very high skilled things or something which increases with experience, rather out of compulsion they are made to work. So the point of getting work experience doesn't seem to remain valid.
And even if we want kids to gain some experience, we can have the courses designed at school to have practical work experience added to the curriculum. Rather than all the theoretical knowledge some hours in a week can be devoted where kids can work as apprentice and learn their desired skill. I personally feel, this decision should also be rather a choice than compulsion. Because children may not be wanting the working experience at such early age and should not be forcefully made to work.
So last not but the least, I think the decision to engage children is relative, where in if children are actually gaining some knowledge or experience should be given an option to work as a part of their regular course and they should not be forced to work at the cost of their childhood or against their wish.