User blog comment:FairyRaven/Fairy Tail Chapter 465: 400 Years, Review and Commentary/@comment-24546844-20151207181359/@comment-24546844-20151207223909

Layla taking care of the kids is only a possible excuse if she knows some sort of memory magic as every kid remembers only wking up and finding out that their parents ar gone. Otherwise Layla was really a bad adoptive mother and just allowed 5 pre-adolescent kids alone (she even separated them) to live by themselves in a world they knew nothing about.

About the key, well, there must be some other way to open it like sacrificing your life or someting like that as there' no way Layla could have all the keys gathered at the time. Maybe she just opened, instead of unlocking it and was there only to take the kids.