Purchase commercial picture mattes that will create a pleasing display when they're placed on your mantel. Use the same size if you wish to display them in a straight line. Small square images work well for this arrangement. Another option is to group a slightly larger piece with two smaller pieces on each end of the mantel. You can also place a large focal piece in the center of the mantel, accented by two smaller paintings on either side. Measure the openings in the mattes and add 1/2 inch. This gives you the size your images should be.
Scan your child's art at 150-300 DPI. An office supply store can do this for you if you don't have a computer, photo editing software or a scanner. Reduce the artwork to the dimensions calculated in Step 1. Print copies on good quality paper. Trim the images so they have a 1/2-inch border.
Remove the backs of the mattes and tape the copies face down over the openings. Make sure the tape is well secured. Replace the backs.
Purchase matching frames. The inside measurements of the frames should match the outside dimensions of the mattes.
Place a frame face down on your clean work surface. Spray the glass with cleaner and wipe it with a paper towel. Flip your glass over in the frame and clean the second side. Repeat this process with each frame.
Place a matted copy face down on the glass. Follow the manufacturer's directions and secure the hardware to the back of the frame. Repeat this process with the remaining pieces of art.
Place miniature easels the length of the mantle. Space them equally apart. Center a frame on each to be able to view your decorative gallery.