When John and company "scratched" their session at the end of Act 5, things changed. Their session and universe were subjected to a cosmic Reset Button, and the resulting rebooted universe wasn't quite like the old one. Many things, both large and small, were different, presumably to enable mankind to have a better chance at winning Sburb. The most prominent change is that the original kids and their parents have switched places, and now it's the guardians-turned-kids who will tackle the new session.