What will they do?

So, looking at the books, through all 4 books, Janner is 12/13.

So, since season 7 will come out in like many years from now, the kid playing Janner (I forgot his name) will have grown up a bit.

So, being older than 13, he certainly wont sound like a 13 year old boy.

So Chris and Andrew will have to find someone else to play as Janner.