Back stories on characters?
Do Sam, Jenna or Goldberg say anything in the movie about how they became able to time travel? The other films either showed or gave an idea that it was in the family line. If so, then Sam's child Jenna could also time jump and probably one of their parents could too.
It would have been a more interesting movie if this was explained. Goldberg threw me off the most. He seemed to know everything about time travel, yet we never see him do it...yet he is almost a mentor to Sam. Without back story, I find this confusing.