I dont get the ending

Yeah dude ... she has them chained up to typewriters in a subterranean cavern and is forcing them to write romance Robles under the pen name of JP McGregor.

From what I understand. She steals kids from poor families that most likely have no bright future and gives or sells them to more fortunate families. Hence Jenny being surprised to see that kid Jason or whatever his name is, who was still alive, but his name was now Jeffrey. Yeah I didn't like the ending, was hoping there was a tall man after all and she was sacrificing them. But you can't always have it the way you want.

you really need to stop texting, and actually watch the movie.

Tracy doesn't have "all the missing children". She has her daughter and granddaughter (born at the beginning of the movie); they've moved back from being with Tracy's sister in Seattle. Oh, sorry, was saying they were in Seattle a spoiler, since you clearly missed that part too?

and Zaltman apparently didn't watch the movie either. Jenny wasn't "surprised" to see DAVID (a main character, how hard to know his name isn't Jason) was still alive. At this point, she fully understood that he would be alive. She didn't even look surprised. She just looked at him, since she knew him, and knew where he came from.