The Sinners Are Much More Fun - S2-E2
Continuity mistake: When Tiffany gets ready to put a bib on Nica to give her breakfast, Nica's hair goes from in front of her shoulders to pulled back somewhat between shots. She's also facing a slightly different direction between the same cut.
Answer: They were blamed for the death of Jake's foster brother, which was deemed a terrible accident, and they were sent to the reform school as a punishment. Presumably, when they had to leave the reform school given what happened, they were instead given community service as punishment.
TedStixon