If you would like a really cool way to make coaster out of leather by dying the leather then here it is. By using dyes in a spray bottle you can get a whole variety of colors. You can use natural scraps of leather, small bottles of in expensive dyes mixed with a bit of water. You may need to use templates to cover different pieces of the leather with different colors. After the leather is dyed you then cut out the coasters in the shapes that you want.

Even though this is written as a more adult craft activity, you can definitely have children that are old enough do the activity as well. Read here to get exact instructions  http://www.designsponge.com/2012/06/diy-project-leather-staining-coasters.html