how did the director get that little boy to cry like that?

I wondered the same thing. So glad they didn't shoot him, his cry had me feeling so sad for him. But in the trivia section, the director reveals that he asked the little boy what his greatest fear was. The little boy said having a toothache. He, then told the boy to pretend that that pain transferred to his foot. I sure hope he never gets a toothache, because he had the snot rolling and everything. I was like 'wow, what really happened?' You figure because of the look of the film, they may have actually harmed him.

R.I.P. Michael Jackson
R.I.P. Heath Ledger

That is a haunting and horrifying scene. Beautifully done, but hard to watch.

You'd cry too