StumbleUpon is a discovery engine (a form of web search engine) that finds and recommends web content to its users. Its features allow users to discover and rate Web pages, photos, and videos that are personalized to their tastes and interests using peer-sourcing and social-networking principles.
Toolbar versions exist for Firefox, Google Chrome, Opera, Internet Explorer, and Safari. StumbleUpon also works with some independent Mozilla-based browsers.
Native mobile StumbleUpon apps exist for iOS, Android, and the Amazon Appstore.
I issued a low rating for threat level. If your child makes an account, he/she selects interests that they will like for stumble upon to find. It locates that category and will show what other people that likes the same category recommended for viewing. You can then view the page and vote if you like or dislike. Then hit the stumble button and go to the next page to view .. Etc
I did rate it a low threat due to being able to follows others that use stumble upon. There are a few categories that you may not want your child to follow. Just be sure to help set up the app initially and periodically see who they are following as friends and what their friends interests are to make sure you approve.
Green, blue, green and blue, s, u, su