Boys and girls come walking up with rollingcarts. At the gate they fold up the cart and make it into a bookbag. Then they put the bookbag on and they go into the school. The area around the gate becomes the bordes between rolling carts and bookbags. Some of the children aren't so good at it yet, they just carry the bag in.
This is a good action to use in some sort of way. Maybe for making imaginary borders visible.