My kids LOVE legos! If it were up to some of them, the room would look like a Lego Store and they would have free reign of building all day. I balance free building with Lego Challenges, not only to keep it interesting, but for them to showcase their mad Lego skills!
The BEST link I found was on Pinterest, there are 51 different challenges and photos of what others created.
Another great link is from Frugal Fun 4 Boys, http://frugalfun4boys.com/category/lego/
For Lego Club:
Each day will have a quick build from the Lego Challenges, sharing creations, as well as time for free building. Due to amount of Legos, creations will have to be dismantled…take photos!