Webelos dens are for boys who have completed third grade (or reached age 10). Webelos Scouts get to work on the five required Webelos adventures and choose two of the 18 elective adventures that are shared by the Webelos and Arrow of Light ranks.
When a boy has done the requirements for an adventure, the Webelos den leader, rather than a parent, approves most of the adventures. For each adventure a boy completes, he receives a pin to wear on the Webelos colors or on his hat. After completing seven adventures, including five required adventures and two elective adventures, a Scout can receive the Webelos badge.
After he has earned the Webelos badge, a Webelos Scout can work on the remaining 18 shared Webelos and Arrow of Light electives until he finishes fourth grade (or turns 11 years old). He can choose elective adventures that may show him new hobbies and teach him skills that will be useful during his Boy Scout years. When he completes an elective adventure, he receives an additional adventure pin to wear on the Webelos colors or on his hat.
Click Here For More Information and Complete List of Requirements & Electives (Cubscouts.org Link)