I saw this film on (possibly) IFC or Sundance in 2006 or 2007. It was in English. I can’t remember the specific source (English, Irish, Australian, Scottish, Welsh), but I don’t think it was American. It might have been a shorter film, but it was not (I don’t believe, at least) an episode of anything.
There is a boy (late preteen/early teen) being raised by his mom. She is a heroin addict who pays him little attention. Her supplier/boyfriend is violent to both her and the boy. The supplier is mad at the boy because he is in the way and trying to get his mom to clean-up. At one point, the supplier takes the boy and locks him in a storage crate (looks like the freight container from a truck) in a secluded field overnight. The kid screams, but nobody hears him. The kid is also harassed by bullies on the way to/from school. At one point, the boy steals the key to the storage unit from the supplier and convinces the bullies to go inside to look at the cool stuff. They go in and he locks them in. He then returns the key. After a number of days of people looking for these missing boys, he makes an anonymous call to the police and they find the bullies dead in the storage unit. The police then arrest the supplier, being that he has the only key. The movie ends with the boy and his mom together.