Help me find the name of a manga

A festa years ago i started reading a manga thats was stating, but the site that i used to read all went down at that time and i kinda became very bussy and didnt look for but now o remeber and want to read the rest.

It was a history about a City that was a prison with very big walls that nobody has ever manage to escape and nobody would get out of there, not even the children that would be bora there. The mc was a little girl Who has a baby brother and would be starving because of a (if a relembrar correctly) death of her father, she would try to steal some food (tha online way to get something in that place) and then she met one group of criminals (that were actuly really nice guys) that would thake pitty on her and left some food in time to time in her door. But that group was planing a escape plane on winter because the security was gona had a flaw because of a snow, and when was that Day, they left a note saying that that box would be the last (i think). I remember that she found out that they would be trying to escape somehow and took her baby brother to try to escape with then but thing got wrong (i dont remeber why) and she fell, the lider made it to catch her but her baby brother fell. They manage to escape but she never forget her brother or lost hope that he would have survive. The next few years the group trained her until she was older, and the she got arrested on purpused to go back to the prison to look for her brother. If somebody knows the nome please tell me i really want to know how is going and how it ends