The still photo, taken from Twitter, suggests that Cyrus' act was too much for the Hollywood star and his young children Jaden and Willow but MTV pointed out that the picture was taken during a performance by Lady Gaga and not while Cyrus was up on the stage.
And contrary to what the picture suggests, the Smiths enjoyed Gaga's act. In fact, Willow's mouth is open because she is in the middle of chewing her gum.