Stamp collectors practice the art of collecting stamps and all of their related articles such as covers, packages or letters with stamps on them. Day of issue sheets are available at post offices for collectors or for use as gifts. It is one of the most popular hobbies with more than 20 million collectors in the United States. Although the stamp was invented in England in the 1840´s, it wasn't until the 1860's that children became their first collectors. Parents at the time thought that it was only a childish hobby, but many of those stamp collectors, also known as philatelists, began to study and do research on stamp production, including the plates used and flaws that may have been made. Collecting stamps is very cool! It can helps kids learn about history, different countries and nations and how they have changed throughout the decades.