Discovery bottles is another great idea for the younger set because everything is sealed in a clear bottle. The bottles can be turned, rolled, shaken, etc. They become look and find for older kids. Easy to theme them according to what you are studying, child interests or seasons. Watch for small things at the dollar store such as in the birthday section, or back to school such as mini erasers, or the craft/scrapbooking section for little flowers and other trinkets.