Super Plothole:Doc. Brown comes back from the future and claims that he needs Marty and Jennifer to follow him in order to save their future children. This is one of the most retarded things ever put on a screenplay. If your children are in danger in the future and you go to the future to save them; when you are coming back to the present nothing that you did in the future changed anything. You will still have to save them AGAIN when the present will reach the future moment.
Since the future is not shaping the present (unlike the past) there is no logical reason to go in the future to save your children…because they don’t exist yet. The only thing Doc. Brown needs to do, is to inform them of what is gonna happen in the future so that they can alter it later.
It could also go further then that. If Doc.Brown comes back from the future and informs Marty and Jennifer that their children are in danger; the simple fact of exposing them that they are going to get married and have kids might destroy the possibility of this specific conclusion to happen.