Hm. I always took that scene as him explaining that the children who rebuilt the world were the Princesses as they were the only ones with pure light still left. But watching it again now, I can see how both readings could work, that the PoH were just some of the children instead of all of them.
Though, at the same time, lol... The world being rebuilt by them alone still makes the most sense to me, as it also explains why they are so important. They are the source of the World's light, as Yen Sid states, and them being responsible for the recreation of the World makes sense in that way. It explains why the world is so hinged on their state. Regular children doesn't really explain that as well.... Eh.
Nothing's wrong with it. It just wasn't my understanding of the scene in KH3D at the time.