I dont think the child thing matters all the much since characters like little red riding hood is a child in the actual version but for Once they made her a full grown woman pretty much for the sake of the story.
But the fact that the mad hatter is already in wonderland when Alice meets him in the story does seem like a too big of fact to over look though. But just some other thoughts for why it could be is that Grace does look sort of like Alice from the cartoon so maybe they are hinting Alice is her mom? Or more likely it was just to draw a connection to the Alice in wonderland story even more since the story we got for Jefferson was full of references to Alice in Wonderland before he actually went their with the queen.
For the sake of discussion than, the only other character that we have been introduced to us so far who has a chance of being Alice would have a greater chance of being would be Grace, which I think most people see as unlikely since her name isn't Alice in either world. If you exclude Grace, which I would like to see someone make a case for her since that would be interesting to read, that pretty much leave Alice just being a new character introduced to us (Which I wouldn't mind at all).
Side note: If the queen of hearts is going to be as important as they seem to be making her out to be than that probably means Alice will be a very important character as well. Perhaps a side kick to Emma, since Emma has been more or less on her own so far.