Book about human-eating bird-like creatures.

I have found similar books but none with the same ending. At the start of the book it's focused on a guy who looks after a young girl. He sees a bird thing eat a homeless man so he goes home to pick her up from school or smth. More people are attacked and rich people are able to escape the birds by leaving the planet on spaceships. A group of kids are sent off by their parents with food and some sort of trolley, the young girl included, because for some reason they have a better chance of survival or something than adults. On the journey they find a village or group of caravan homes and an older male kid enters one of these homes to search for food and inside(in the dark) are the bird bat things and they attack (and maybe kill) one of the kids. Eventually they reach a mountain and cave? With other creatures that kinda give them a place to stay. Maybe this is multiple books that I've combined in my head? Or a dream? And I think it comes from a book with multiple stories in but I don't think that it's “The Birds” by Daphne du Maurier. I read this at age 10 (9 years ago) so that's why this description is so atrocious. any help would be greatly appreciated!:)