Perhaps you are not familiar with the "Make a Wish Foundation". It's a non-profit that aims to bring some joy to the lives of children who suffer from life-threatening illnesses by granting their wishes. Many celebrities get involved in such programs because so often the wish the children want granted is the chance to meet their favorite celebrity. As you can see from the video, several of the girls are wearing Make a Wish T-shirts. That and the fact all the interaction is taking place in a children's hospital should be a dead give away that he's involved in volunteer work with that organization. To be sure, I looked it up: http://www.wish.org/stories/sports_entertainment/music/monroe_justin_bieber sure enough, 4 of the children in the video met Justin through that organization.

As for whether praying makes sense or not, we just had that discussion several weeks ago. See here: https://www.cblf.org/messages/64060.htm.

If you don't believe prayer works, then you don't believe in the teachings of Jesus. Jesus not only taught us about prayer with words but by the example he set in living a life filled with prayer.

Luke 5:16 But Jesus often withdrew to lonely places and prayed