In case you haven’t seen Bird Box yet or watched any of its previews, just like the same-named book by Josh Malerman, the movie stars Sandra Bullock as Malorie, a mother who has to take her children, simply called Boy and Girl, through a forest and across a river to reach a new place to live, and they have to do all this while blindfolded. The reason for this is because there are monsters that have come to Earth that, when seen, force the viewer to either kill themselves or become servants of these demonic entities. As for why the movie is called Bird Box, that’s because birds can sense these monsters without seeing them, making them handy alarm systems.
Article source: https://www.cinemablend.com/news/2464420/netflix-had-to-issue-a-warning-about-the-bird-box-challenge