This is a "no equipment" tag game and is one of my scout section's favourite games. As the leader you can make life fairly easy or very difficult for both cat and mouse.
Whistle, but not essential
One scout is the mouse, another the cat. The rest of the scouts form a square with equal lines. Think noughts and crosses where there would be nine scouts. This can also be played with sixteen, twenty-five, thirty-six, forty-nine scouts and so on in the square otherwise you will have a few gaps - or you can have a rectangle. Scouts all face in the same direction and raise both arms so they’re horizontal. Scouts then space out so that finger tips are touching. Now let the cat and mouse loose in different parts of the square. The aim is for the mouse to be caught by the cat by being tagged. Cat and mouse can run up and down the rows or round the outside of the square but not under the outstretched arms. When you shout “Change!” or whistle all scouts must turn 90 degrees clockwise. This changes the rows by 90 degrees and can seriously disrupt a cat who may have been almost on top of a mouse. Similarly, if the mouse was miles away, it might now find itself in the same row. When the mouse is caught, or after a certain amount of time swap cat and mouse with two new scouts.
Variations: Gaps placed in the rows will provide added excitement. Use an extra cat and / or mouse. Play for team points.
From "1000 Fantastic Scout Games"