We always have our preschoolers pick up their own mess. Obviously they are 2.5-5 year old's and things do not always get put back where they belong. So instead of spending hours every Friday resorting things when it gets bad, we have the kids help.
We dump out messy bins that contain items that don't belong in them and have the kids find the right home for them. We have to do this about every two weeks. Slowly as the year goes on we see kids putting things away in the wrong place less and less because they have figured out they are going to have to help sort it. This helps them learn where everything is as well.
We also have the kids wipe down tables and chairs. Cleaning is an important responsibility to learn. I know we have had several parents realize their children are cleaning and helping at school and they begin to see their children should be helping with chores at home as well. Children learn through doing, and cleaning is a hands on activity. They are learning Small and Gross motor skills through household and classroom chores. So cleaning is learning!