Stupidity: There is no way Mr. Mertyle did not hear the fence in his backyard crash to the ground; there's also a likely chance he could hear his dog crying and Smalls saying the dog is hurt. Even if he could ignore the sounds of other attempts to try to get the ball back; with the fence coming down where his dog lives and the chances of an injured pet it seems far too unlikely he wouldn't have rushed straight to the backyard hearing this.
Stupidity: If the fairies knew that Maleficent was going to try and kill Rose on her 16th birthday, why, oh why, do they take her back to the castle on that day? Why take her back to where Maleficent was expecting her? Why not wait until after her birthday?
Stupidity: Billy and Allie saw there were several men in the area also searching for the medallion and the kids even hid from the men minutes before finding the medallion. Instead of quickly sneaking away after they found the medallion, Billy and Allie stayed in the same spot and Billy shouted, "We found it! We found it!" Seconds later, two men came from behind the tree. (00:24:00 - 00:24:21)