For what it's worth, I'm standing by my assumption that Boy 2 is Digory, as that feels like the better paired description to match what is presumably the "Polly" role.

This is partly based on everything we've seen in terms of the casting process so far, the sorts of people who have applied for the two previously advertised roles, and the overall symmetry of the Polly/Digory and Frannie/Isadore configuration that was used in the original casting call.

But tackling the broader question of who the "other" boy would be, regardless of whether it's Boy 1 or Boy 2, and given that it in either case it's for a "lead" role, I don't buy the idea of it being a small flashback to Andrew as a child, since that feels way too brief and insignificant to be comparable to Polly's role.

I'm thinking it's more likely an original character along the lines of "Gael" in the Dawn Treader movie.

Possible examples:

• A random street urchin they find on the streets of Charn who provides some background exposition and tags along for a portion of their adventure.
• A brother or sister for Polly or Digory, possibly added for the purposes of getting killed off at some point to raise the dramatic stakes.
• An orphan from the real world who lives in an orphanage with Polly (thinking back to the Frannie dialogue where she says that her family is all dead and she's not like all the "others")

For Boy 2 I can only assume his role is a younger Uncle Andrew. If not he's either Polly's brother, a neighbor, or Helen and Frank's son. I know people have also thought it possible as a voice over for Strawberry/Fledge which I think isn't the case at all. I think casting would've put in the description if it was a voice over. They're looking for a human boy close to Digory and Polly's age.

The boy could also maybe be Letitia Ketterley's son. While she's said to be unmarried, maybe they could adapt her character to being divorced (controversially at the time) or widowed or even having a son out of wedlock? it might add backstory to why she became "a very tough old lady"?

Posted by: @rilianix

The boy could also maybe be Letitia Ketterley's son. While she's said to be unmarried, maybe they could adapt her character to being divorced (controversially at the time) or widowed or even having a son out of wedlock? it might add backstory to why she became "a very tough old lady"?

This can be a possibility as well. Though because all children are around the same age I still find it likely it’s younger uncle Andrew. He states in the book if I remember correctly when he was Digory’s age and told the story of Mrs. Lefay.

How about this for a theory. The have decided (for whatever reason) to make Digory Anglo-Indian and they don't want a non white character to be one one responsible for awakening Jadis and bringing her to Narnia. So they've created a new white boy character who will join Digory and Polly and take the 'villainous bits' in Digory's original story. 

Of course, if true, this would undermine the entire moral structure of the original story. 

I am inclined to think that the boy of Indian decent is Digory, and as some others have suggested that the other boy could be a flashback of Uncle Andrew.  Although, I also have another suggestion for the other boy which, I don't think anyone yet has suggested, and is quite fitting with the book - although perhaps a plan to expand the role a bit - I'm thinking the butcher's boy.  I'm aware he only has one line in the book - but perhaps an expansion of him in that scene?  

Posted by: @pete

I am inclined to think that the boy of Indian decent is Digory, and as some others have suggested that the other boy could be a flashback of Uncle Andrew.  Although, I also have another suggestion for the other boy which, I don't think anyone yet has suggested, and is quite fitting with the book - although perhaps a plan to expand the role a bit - I'm thinking the butcher's boy.  I'm aware he only has one line in the book - but perhaps an expansion of him in that scene?  

Nice catch @Pete  

I was trying to think of anything I may have missed in my recent reread of the Chronicles. Could definitely be a expansion on the butchers boy too. I wouldn't mind on expanding smaller characters. I said the same before about Gwendolen on Prince Caspian.

So I've been considering these roles some more by also looking at the dialogue in the audition scene being used, and whether it might inform the "mystery of this other child". So, I'm intrigued by two aspects to the script. Firstly, these lines;

"ISADORE: Will you give it back after?

FRANNIE: Of course, I’m not like all the others."

Who are these "others" that Frannie speaks of? Is there a chance this other child could be someone who Isadore (Digory) doesn't like or get on with? Maybe there's a group of children who also live nearby who treat Digory, and maybe Frannie (Polly) poorly? Therefore could Boy #2 be one of these groups of children, a main "bully" perhaps? It's a bit The Silver Chair-esque, in terms of the two main characters being bullied, but could still be applied here if they wanted? I think it would make sense for both Digory and Polly?

The other lines that interest me, and could maybe lend themselves to there not being a new young character, who becomes part of their journey to Narnia, are these;

"FRANNIE: I don’t have any friends, I won’t tell.

ISADORE: I don’t have any friends either.

FRANNIE: You do now."

Now, this could be a pointless exercise, given how we don't know the importance of the dialogue and its specifics. For example, the discussion over Isadore's name doesn't really align with how the discussion would go down with the name Digory, but I still think the lines could hint at the main focus, and main dynamic of the film, still being Digory and Polly, with again, no new character being thrown in with them?

One of the things that causes Polly and Digory to become friends is that neither of them has gone to the seaside (for the long summer holiday), while apparently Polly's friends have all gone away.
Bringing in a third equal friend reduces the reason why these two spend so much time together.
Whether Digory is played as Boy 1 or 2, the other boy is not part of their games and exploration.

It's also a good thing to note that some audition sides have nothing to do with the project or a scene in it. It's written to test chemistry between actors who will then get into the next round of auditions. Big productions like to save the real screenplay when they are down to a few choices to cast.

And I totally agree with that @Coracle

I kind of think at this point you have to take the original casting call at face value, in that it was clearly for two roles only, both of which were described as "important", and both were open to any ethnicity.

We've also determined that those two roles bear the code nanes "Frannie" and "Isadore". Therefore its a fairly clear piece of logic to form:

Isadore = Open Ethnicity = Boy 2

The other side of the equation is

Boy 1 = British Indian Ethnicity.

Therefore I think you either have to go with Digory = Isadore, or Digory = British Asian... I'm not sure you can make both fit without some additional leap in logic to get between the two.