Random side note, but the Daytime Emmy Awards have long had the categories "Outstanding Younger Actress in a Drama Series" and "Outstanding Younger Actor in a Drama Series."
I think it makes perfect sense that someone could be a great child actor but a rather average or even sub par adult actor. We expect different things from children and adults and some people may be better at one or the other. Plenty of kids did some bad acting but went on to great success as adults with some real talent.
"Michelle would never be caught with sausage grease staining her Vera Wang." - rfisher
Other critics' awards already have younger actor categories:
For example, this year's Broadcast Film Critics' nominees in the younger actor category are:
Best Young Actor/Actress
Super 8: Elle Fanning
The Descendants: Shailene Woodley
Extremely Loud and Incredibly Close: Thomas Horn
Hugo: Asa Butterfield
Hanna: Saoirse Ronan
We Need to Talk About Kevin: Ezra Miller
Note that Woodley was nominated for a Golden Globe for supporting actress last night and Ronan was nominated for Atonement 4 years ago.