Train Quest (2001) on Netflix

Plot summary

Billy is a boy who comes into the local model train store, and his older sister is Ellen, the girl August dreams about. August is fifteen and handles the assistant manager duties there by himself. After an evening out with Ellen, the two of them stop by the store, and August shows her the train set and the model city laid out in the back room. He sets the passenger train running. The set zaps the two of them, shrinks them down and puts them aboard the train itself. Mr. Dalby, who owns the shop, gave August the use of the back room.