A simple way for someone to make a magnifying glass is to use a clear plastic 2-liter bottle and water. It is necessary to cut a circle near the neck of the bottle, then use that concave piece to hold some water. The magnification effect is seen when it is held above an object.
The plastic bottle and water method is one of the easiest ways to make a simple magnifying glass. It is a hands-on method of showing the science of refraction and magnification. Because the disc that was cut out of the bottle curves out, it is a convex shape. When the water is added, that creates a refractive effect, bending the light inwards and enlarging the object.
For a project a little more involved, the supplies needed are a small embroidery hoop, a plastic bag and a hot glue gun. Have the child fill the plastic bag about 10 percent with water, and seal completely. Then, lay the bag out so the water is centered in the middle inside the bottom hoop, and then place the other embroidery hoop on top and tighten securely. Pull the bag until tight and then trim the bag around the outside of the hoop. Seal off the seam by beading hot glue around the edge. The water inside the bag creates the magnification effect.