P.1 xmen timeline

In this short clip from the film Xmen there is never dialogue and voice over at the same time because of the obvious reason that if you do that you wouldn't be able to understand anything as there will be two voices talking at the same time.
The music plays all throughout the clip to make it flow as the clip as a lot of different locations and it would sound quite rough listening to all the different background noises. This is why music just mutes the background noises a bit so the music goes over it. The music also tell you the environment of the school, it's a calm and nice music.
The special effects are important as it would be rubbish without them. You wouldn't hear the ball bouncing on the floor or the ice falling on the ground and breaking. It would look like a simple clip with just digetic sound music and a clip.