Kids can sort seeds coming up with their own categories, they can sort flowers the same way.
To make this activity most effective, allow students to come up with their own categories. A good way to do this is to create a grid that has squares big enough for the largest item they are classifying to fit in. Have the children write the category title at one end of each column, then place each of the objects that goes in that category in a square in that column. After all of the items are in place, students can color the squares that were occupied. They then have their very own bar graph.