Hello all firstly , well basicaly I cant remember the name of this film for love nor money so heres a vague description.

Well basicaly a group of people are in an underground / semi secure location , variety of people ofc a few men and a few wemon also young boy and a teenage girl that later becomes 3 (found young boy).
ok plot - most of the movie you are aware that early night time restrictions on leaving rooms are in place becuase of some frosty creature roaming around during the film getting earlier and more frequent. most of the time they spend this night time with 1/2 people in rooms freezing the asses off.
and there are daily experiments that these older people are fruitlessly trying (if i remember right)
ok next thing i remember properly is the group have to go out and get supplies which get more and more risky, braving men / mosters types that tbh want to kill them.( i realy cant remember) a few die on the excursion and things just get worse for the group.
there is also and outsider to the group (i think hes "outsider" because he knows truth or just cant be arsed with the groups efforts)
the kid that the child goes roaming around in restriced zones and finds another kid that survived in the "forbiden" zones for far to long.

skip to end as i dont remember to much around here - basicaly all that survive have to leave there safe zone and end up outside, to where they all reside to dying from many monster types surrounding them pannig out to reveal to the kids that th world is already well past its end and is fragmented and there living / surviving on a chunk of it i belive.

lol well thank you for the effort in reading this monstrosity of a memory of a film lol ,have a good chuckle then any help identifying it if it rings any bells would be great thankyou.