She wouldn't quite be the youngest Oscar nominee ever; that status still belongs to eight-year-old Justin Henry, who was nominated as best supporting actor for Kramer vs. Kramer in 1979. (There was also Jackie Cooper, who was just a shade younger than Wallis when he was nominated as best actor for Skippy in 1930.) But, crucially, Beasts of the Southern Wild took a few years to reach the screen. Though she's nine now, she was a mere six when the film was shot. To put it another way, she was not quite seven, which is the year developmental psychologists like to refer to as the age of reason: when kids start making decisions based on logic and causality. I'm no psych expert, but it seems to me this might be the sensible cut-off point for acting plaudits.
Acting requires some intentionality on the part of the actor, some conscious effort to adopt a persona other than his or her own. Even adult actors who get criticized for "playing themselves" are engaged in a series of more or less conscious decisions about how best to be themselves onscreen. A young child, meanwhile, likely isn't thinking at all about how to be herself, let alone a character. She's a kid, and she just "is." This is, of course, a big part of what we're responding to when we watch Wallis: her innocence and her lack of self-consciousness. She feels genuine precisely because she's incapable of being otherwise.
It comes down to what we mean when we talk about a great performance. Do we simply mean the performer in question entertained us? That they're unusually magnetic, memorable, and enjoyable to watch? If so, Wallis shouldn't just be nominated, she should take the trophy. She's hugely magnetic, and she commands the screen to an extent most adult performers could only dream of. But what she does in Beasts is not acting. What she's doing is being a great camera subject.
It's questionable, too, whether nominations even benefit child actors. If acting awards are to exist at all, they should probably have some sort of practical value. For instance, a nomination could help an actress who's been toiling in the trenches and really needs a boost—someone like Mary Elizabeth Winstead of Smashed, or Emayatzy Corinealdi of Middle of Nowhere. Conversely, if a nomination can encourage an established star to shun fluff for more demanding roles—like Matthew McConaughey in Bernie and Magic Mike and Killer Joe—then that's great, too.
But nominations for wee children? Maybe it'll be great for them and maybe it won't be. They will almost certainly land more parts—indeed, Wallis has already scored a role in the upcoming Twelve Years a Slave—but for how long? Kids who don't grow up to have the same charisma they had when they were younger may find themselves washed-up before they're even able to drive. (Seen Haley Joel Osment in any movies recently?) Also, it can't be healthy for a young child to go through the months-long orgy of adulation that is the modern Oscar season. It isn't even healthy for the adults who get nominated. If what we loved about Wallis in Beasts was how "real" she was, why are we so eager to turn her into another Tinseltown success story?