Why did Game of Thrones decide to hire teenagers to play the role of teenagers, rather than youthful-looking adults?

The fact that they are children is very, very very important. It's key that these children, raised in a warm happy home in the frigid North are ripped from their native element and subjected to all kinds of horrors and travails and trauma: because it's about their development as people.In the books they are even YOUNGER. Jon Snow and Robb start the books at 14, Sansa at 11, Arya at 9, Bran at 8 and Rickon at 3. And in the books, only about 2 and half years have passed in-world. Obviously we are on our 6th year in the show, so the actors, who were already young to begin with have grown 6 years: most of them may be legally adults now. This is a just a reality of shooting such a sprawling epic over many years. It would be impossible for the shoot to cover only 3 or four years as it will in the books and, yes, the children's growth into adults does sort of undermine the story a bit, but there's nothing that can really be done about it. I don't think the shooting schedule has been affected by that so much as many many other practical, legal and logistical matters have shaped it.

It's because teenagers are portrayed by young adults is why they chose to actually use child actors.  That and the characters of Sansa and Arya Stark are 12 and 9 respectively when the series starts.  I don't care how young some 25- 30 year old looks, they're not going to pull off 11 and 9.  So, GoT did the right thing and actually cast two people closer to the ages of the actual characters they were portraying.  Had they instead used someone twice their respective ages, the outcry would have been deafening."YOU MADE ARYA STARK 18 YEARS OLD IN GAME OF THRONES?!?!  HAVE YOU LOST YOUR MINDS?!?!"Not only would it have ruined the characters, but it would have removed all importance of the characters themselves.  The Starks' ages are crucial to the development of the story and making them teenagers, when only two of them are in the books, because it's what's been done in the past, would likely have destroyed the show before it finished it's first season.Plus, people have been bitching for years about this very thing."We're supposed to believe that the married dude with three kids and a full beard is playing a 14 year old boy?  Yeah right, at least cast a teenager to play him."So no, casting age appropriate people to play characters that are close to their own age would not hinder the filming schedule, if anything it makes it easier, as the actors can better relate to the characters, as opposed to some 30 something year old who has no idea why the character is doing something so childish.  At least then you're not getting a conversation like:Actress: "So my character likes to play with dolls and dream of dreamy princes?  What is she, 12?"Director: "Actually, she's supposed to be 11."Actress: "But I'm 34!"Director: "What's your point?"Actress: ".............."