Good afternoon all, I find myself in a predicament: I'm writing for 8-10 year-olds who, as I understand it, are very dependent upon dialogue to keep the story engaging. Unfortunately the protagonist of my story and his family are proto-humans who have sign language but not yet developed sophisticated speech. Is it possible to keep children interested without intermittent dialogue and are there any good examples of this that you can point me to? My alternative is to anthropomorphise them like Fantastic Mr. Fox but I'd like to go for realism wherever possible.
Speech is simply communication. Your characters communicate and all you need to do as a writer is make clear what is being communicated.
I once read a fantastic children's story to some children. Teddy never actually says anything but communicates on every page.
"We should get biscuits to make us brave" said Joe.
Teddy indicated that he agreed.
The cat looked at them suspiciously
Teddy hugged Joe so that he would not be frightened.
Teddy pointed to the light switch to show Joe that ...
That sort of thing happens throughout the whole book. Teddy has a lot to "say" an yet never actually speaks.
In your case I know that you are aiming for an older audience but the principle of showing and reporting to give communication even when it is non verbal is the same.
As I understand your aims you can actually go much further than "teddy" and make the readers feel like they are part of the culture.
The wolf howls were getting closer.
Big Man waved his hand next to his ear too indicate hearing. His face said that he was worried.
Tall Man touched his nose to indicated that he understood and pointed towards the cave. He nodded to the other men and made a pushing gesture towards the cave to show that they should enter.
As long as you are consistent with the sign language used your readers will be smart enough to only need to have you interpret the first few times the sign is used. If, as per my rough example, touching the nose happens a lot then later you might only need something like:
Big Man grimaced. He patted his empty stomach sadly.
Tall Man touched his nose and pointed to the old man's bag.
Nothing is being said verbally here and no translation has been offered but given the previous context we know what is being said and what is being suggested in reply.
As another answer rightly points out sign language is speech. These characters are talking to each other the reader just needs you to translate enough for them to follow along. There are a number of ways you can do that and each one has its own benefits and restrictions.
As any deaf person will tell you, sign language is speech. How else are you going to tell your story if you don't report the communication that does take place?
Bearkiller signed: "Walk quiet. There is a mammut ahead."
Darkwalker nodded. "I'll circle to the left," he gestured. And don't argue about this again, his face said.
Bearkiller frowned, then nodded. Okay. "But wait until I have the fire going," he signed, then turned and crept away.
Handle sign language and facial expressions in the same way that other authors handle foreign languages. An English language novel that takes place in China does not contain Chinese dialogue. The speech of the Chinese is quietly translated into English by the author, and the reader has to imagine it being in Chinese.