Young children love the sword and sorcery of the medieval knights of legend, so a knight costume is perfect for your child's fancy dress party. Try studying pictures of knights of old to get the details right, and ask your child what he would prefer painted on his armour. Heraldic lions, dragons and unicorns were all common features of medieval armour so you and your child can have fun coming up with the perfect theme for his armour.
Measure the breadth of your child's shoulders, add 2 inches to this measurement and cut a square from the sheet of thick cardboard matching this measurement. In the centre of this square, cut a circular hole large enough for your child's head to fit through. At each corner -- about 1 1/2 inches in from the edge of the cardboard -- create a small hole with scissors or a hole punch.
Bend the cardboard over your child's shoulders and connect the two ends of the cardboard by threading string through the holes and tying a knot. Remove the cardboard from your child's shoulders and spray with the silver metallic paint.
Cut six more strips of cardboard the same length, but this time, 4 inches in width. Cut holes in each corner of the cardboard -- again about 1 1/2 inches in from the edge -- and spray paint these strips with the metallic silver paint. Connect these into two sets of three by threading a piece of string through them in an over and under fashion. Tie a knot in the bottom of each piece of string and thread the top through the holes in the bottom of the shoulder plate. This should leave you with a central shoulder plate and three plates of armour beneath it on the front and back.
Spray the exposed string with the metallic spray paint and leave to dry. Using the acrylic paints and a brush, start painting the detail on the armour, for example; a fleur de lys pattern, a heraldic lion or a unicorn.
Cut an old plastic soccer ball in half and cut out a length of thin cardboard, 1/3 the diameter of the soccer ball and 4 inches wide. Staple this to the cut edge of the soccer ball so that it hangs beneath it. Cut a bowling pin shaped piece of stiff cardboard -- this should be about 3 1/2 inches long -- and staple it to the middle of the other side of the soccer ball. This will be the nose guard.
Spray the whole thing with the metallic silver paint and then let it dry. Using the acrylic paint and a brush, paint on detail and decoration; you could include rivet details or small patterns like on the main armour.
Have your child put on the grey trousers and grey long sleeved sweater. Place the armour over his shoulders so that his head is protruding from the hole and place the helmet on his head.