I think I listened to this as an audiobook two years ago, so I'll be trawling through my history, but the main character (who I think had a non-standard female name) is a middle or high school student in the United States. Her family had recently moved to the town after her mother's death (maybe in a plane crash?). One of her prize possessions is her mother's digital watch, which no longer works. Early in the book, she encounters a seemingly crazy woman by a creek who gives her a book with a somewhat pretentious title like The Book of Little Things. I think there's another new girl in the school who she considers somewhat uncool, who tries to make the protagonist her friend since they're both new girls at the school. Said new girl has a talent for freeclimbing due to having done a lot of rock-climbing gym work at her old location. The action of the book gets kicked off when their class does a school trip to a local farm (which is nearby the aforementioned creek).
While at the farm, another classmate (a football player?) takes interest in the protagonist, but she initially thinks he's making fun of her. The protagonist also notices that there are a lot of scarecrows on the property, with their hands made out of forks and gardening tools, and at times, she thinks that she sees them move out of the corner of her eye. I think one of the people in the class disappears during the trip. They also learn that there's a tragic backstory to the farm where the owners of the farm (maybe about two generations back) made a bad deal with something mystical and their children were carried off. When trying to leave the farm, she notices that the bus driver looks different, wrong, more monstrous, and then the bus stalls out and they notice that the fog has rolled in and there are a lot more scarecrows. I think one of the teachers goes out to investigate and disappears. The bus driver is acting creepily, and the protagonist's watch starts beeping as if an alarm was going off, and displays a short message (maybe "HELP"?) and then a countdown. In conversing with the driver the protagonist becomes convinced that he is with the enemy, and she decides to set out on her own, accompanied by the other new girl and the guy (or maybe she runs into the guy and he works at the farm?).
From there, I think they wind up being pursued by the scarecrows, and initially hole up in a farmhouse, which turns out to contain the ghosts of the previous owners (including the children who were lost?), and they learn that the book is part of how these deals are made, and they later make their way to a barn where the other girl's climbing prowess lets them get into a loft before the scarecrows can catch up, giving them a chance to rest. I don't remember how they escape in the morning, but I remember that they find a first aid kit, and are able to patch up the scratches they've picked up, and I think one of them is carrying food. From there, I don't remember how exactly they wind up in the next location, but somehow they wind up in a corn maze, separated from each other. And I think the real bad guy, the spirit that the other family bargained with, shows up in the shape of a boy her age and basically offers her the bargain that he's willing to play a game with her of her getting to the heart of the maze before his hound (who is the bus driver) catches up, and he'll free all three of them, or she can choose to go home by herself and leave the others behind. She chooses to play, and uses signals from her watch to navigate.
She succeeds, and gains some grudging respect from the villain and they all find themselves making their way out of a field, the fog fading, their phones suddenly working, and they're able to be picked up. I think the teacher got back to the bus after they left, and the bus started again, and these three have been assumed to have gotten lost on the farm. The watch goes dead again, I think after putting up a display of "LOVE", and they go back to normal life, having become fast friend through shared adversity.
There was a sequel where they go on a ski trip (the three kids, the protagonist's father, and I think maybe the boy's mother?) and wind up at a haunted resort that turns out to have used to have been some kind of orphanage. My memories there are more scattered... I know there was something about a warning to not look into mirrors. There's a ghost in a ski-suit who seems to be a teenager who froze to death on the slopes. Shortly after they arrive, they learn that the resort is under new management. The storm gets worse and they lose power (and the backup generator turns out to be bad, I think). The main villain seems to be the matron of the orphanage, who manages to trap one of them in a closet at one point, which they later learn she used to do to children under her care as punishment. Ultimately, the real villain is the one from the previous book, who is still playing games with them. There are various taxidermized animals at the lodge, including a bear and some beavers, and they keep changing positions when no one is looking. One night, one of them (or maybe more of them?) gets trapped on the other side of the mirror, having decided that the warning was false, and they have to solve the mystery without being able to directly communicate. I remember the climax involved a room with beds where the various ghost children slept, their eyes frozen shut, with a protagonist trapped in there with them, and they found a way to break them out of the mirror by setting a fire that's on both sides, or maybe forcing a situation where it appears on one side. They succeed in getting out safe, some aspect of the matron's curse is broken, and the storm gets better. They convince their parents to end the vacation early, and they go home. I think there were hints that two of the parents were getting a bit romantic with each other. I also remember it feeling a bit odd to me that there was no romance with the guy among the kids, and one of the girls, just because it's rare for authors to not try to pair people up.