The northern girl must be straight-talking and fearless like Lyanna Mormont
For the girl, they’re specifically looking for someone northern, between the ages of eight and 10 (sorry southerners) so it’s pretty damn likely that she will join one of the houses in the north.
She must be straight-talking, fearless and strong minded, so think Arya and Lady Mormon rather than a young Sansa or Myrcella.
The GoT community news website says:
“The role is described as being a straight-talking Northern-accented girl, someone remarkable for her dauntlessness and integrity.
“According to the write-up, she’s been brought up in a family of soldiers and shares their fearlessness.
“The part is said to be a ‘very nice stand-out part for a strong-minded young girl with a fighting spirit’.”
The site goes on to suggest that it could be a flashback scene of a very young Lyanna Stark – Ned’s sister and mother of Jon Snow, who died shortly after he was born.
The current plan for filming the northern girl is during the week commencing November 17th.
The boy could be a young Varys
The second part is a “physically fit and agile” looking boy, aged eight to 12. There is no mention of accent, which pretty much rules him out of being from the north, but he is described from being from a poor background, he could easily be see popping up around Kings Landing.
Maybe a young Varys? His back story is yet to be properly revealed. We know he was born a slave and travelled around the Free Cities until his master sold him to a sourcerer who... well we all know what happened next.
There is no mention of hight or colour, but he must also be available for filming the last week of November and the last week of December.