Why must members of this society do volunteer work while they are young?

There are, I think, a couple of reasons why the kids have to do volunteer work when they are young.

I think that part of it is that the community needs the help.  It seems like maybe the community does not have enough resources.  It never actually says this, but it seems like it to me because they collect all the scraps after dinner and they use the kids for work.

Another reason, I think, is to help teach them to be responsible to the whole community.  I think the volunteering emphasizes to them that they are necessary to the community and that they have a responsibility to be of help to the community from a young age.

But more importantly, they have the kids do volunteer work so they can figure out what the kids are good at and what they are interested in.  The elders pay attention to what the kids do for their volunteer work as an indication of what they should be assigned to do once they become Twelves.