Red Group - Find some 2D shapes in your house and garden. Make a list of all the squares, triangles, rectangles, circles, pentagons and hexagons you can find. Then with some sort of building material (Lego, Mobilo, K'nex or even playdough) make those 2D shapes.
Green Group - Find as many different right angles, acute angles and obtuse angles that you can in your house and garden. Make a list of them all.