User blog comment:FairyRaven/Fairy Tail Chapter 426: Black Heart, Review and Commentary/@comment-25111584-20150330130145/@comment-25111584-20150330130845

They most probably are, which would make it even better. Mary is quite an innocent and lovable child, wanting to be with her sister. Here, she's a cute psycho. \(^_^)/

On the other hand, Mary should be older. Not to mention she doesn't really seem to remember Gray or Gray her. So there is room for doubt.