Time Travel is so confusing??? (Spoilers)

I hate time travel movies because the more I think the messier the plot becomes....like as Osment travels back to 1946 to tell his dad about the outcome of his disappearance and how they are stuck in an alternate timeline and only him going back can fix everything...so the dad comes back....now if everything has returned to normal Osment never worked on the time machine and neither did he went back to 1946....so who convinced the dad to leave 1946 and return back???? and I couldn't find any scene between grandfather and Osment discussing this sort of paradox...