Doing so is a great way to foster outdoor exploration. The concept here is simple - every time you're outside with the kids, ask them to find something special to put in the nature bowl. This is especially exciting when you're on vacation some place new but it can also serve to make the mundane backyard interesting again.
You can use anything from a fancy serving bowl to an up-cycled food container to collect your treasures. Then, whenever your children find something new (a seashell, leaf, rock, etc.), add it to the bowl and spend a little time talking about the object. Discuss things like it's physical properties (big, small, smooth, sticky, rough, etc.) as well as where it comes from and what role it plays in nature.
Older kids may also enjoy keeping a corresponding journal where they can keep pictures and descriptions of their finds. By the end of summer you will have a diverse collection your kids have enjoyed curating that looks pretty on your console table.