>>987625401. It makes the second movie just the first one
2. That little change just screams of "Girl power! Because girls can do as much as boys can and we have to shove it, it is 2018 after all!"
3. The parents already had their time to shine, we know their past and their present, it's time for the kids to have the screentime(sure they had a small arc in the film, but it was just shoehorned in). This is why people are angry that there is no timeskip, because there are countless interesting stories you could make out of this.
This is why most sequels are being looked down upon, because they don't try to do anything new.
Imagine if in back to the future, they didn't go to the future or to the wild west in the second and third movie, but just go back to 1955 again, because "it happened in the first movie, why are people freaking out about this?"