While most of the children were cast through open casting calls, LaKeith Stanfield was the only actor to return from the original short film Short Term 12 (2008). Director Destin Daniel Cretton had to struggle to reach him during the casting as he had quit acting and did not have a cell phone.
It was due to her unpretentious character portrayal in this film that director Lenny Abrahamson cast Brie Larson in his acclaimed Raum (2015) garnering her a Best Actress Oscar.
After reading the script, Brie Larson tried to convince director Destin Daniel Cretton to cast her by telling him that she had applied to volunteer with disadvantaged children to research the role. Cretton was impressed, and Larson did not reveal until later that she had been rejected by every organization to which she had applied.
The song featured in the film, "So You Know What It's Like," was originally written by writer/director Destin Daniel Cretton and then re-written by LaKeith Stanfield, who is also a rapper and sings the song in the film, in an attempt to incorporate his own experience as a child into the song and make it more effective.
Destin Daniel Cretton wrote the rap music in the film, and then, according to him, LaKeith Stanfield touched it up and "made it better."