Unfortunately it is too often true that the worst behaviour in the audience comes from the entourage of the "headline" performers who show no respect for the artistic talents of anybody else.
As for the boy playing on his game, as long as it was not preventing others hear the concert I have no problem.
Our twins are now 6 and love folk music. That said, they have a limited attention span especially when tired. Often we need something to take up the slack in their energy levels. Colouring books in a corner are useful, but a small quiet electronic game will keep them silent for longer. We still find them singing choruses the next day, so it doesn't prevent them taking in what is sung.
Quack!
GtD.