FirstLoveMovies

https://www.imdb.com/title/tt12935234/

Sage is a young American woman working in London as a babysitter. She gets called in to watch over two little girls, who are delightful to babysit. But as the day wears into the evening, Sage starts to feel something amiss, as small signs and unreturned messages add up to a more ominous meaning.

But when the girls' parent fails to return at the end of Sage's shift, Sage's protective instincts towards her young charges take over as she attempts to get to the bottom of the looming crisis. But what she discovers is much more surprising than what anyone thought.