Sucked into an altered past

This is from the NaNoWriMo Adopt-a-plot folder where writers post extra plots they won''t be using.

#4: Three kids are sucked into a European History text book, and land in a very different version of history and the only way they can escape is to change things back. Everytime they do, another piece of the path home appears. -- Seadragon

Use it as a 10-15 minute writing prompt or go for a longer piece.