He's Out There (2018) on Netflix

Plot summary

Laura takes her daughters Kayla and Maddie to a lake house in the woods for the family's yearly vacation, with her husband Shawn due to arrive later. Owen, who lives in the area, says the son of the family who had the house before them went missing. Shawn buys a music box for the girls at a gas station. Outside, Kayla and Maddie trail a long red string into the forest and find a tea party laid out with two cupcakes; Maddie eats one while Kayla saves hers for Shawn. Maddie falls ill that night and throws up a scrap of ribbon marked hello. The cupcake her sister kept holds a second ribbon, reading goodbye.