'Room' also faces a popular dilemma for writers. How do you write as a child? Literature is littered with highly critical reviews of children as first person narrators. It's difficult to remember how limited a child's vocabulary is at different life stages and also to consider how that would impact on their reasoning. Invariably the author will slip, either in word choice or self-awareness. 'The End of Everything' has a teenager as the central character then adds in the complication of making her an unreliable narrator, and using memory to smudge the timeline. Again, the use of a younger character means part of the reader will always be thinking 'is this accurate?' 'would someone of that age really say/think/do that?'
Knowing that the use of a younger narrator will mean your work is subjected to a different type of scrutiny is not a reason to avoid it. However, it's probably best to be aware that someone somewhere will criticise your narrator's word choice, points of reference or self-awareness. Unless, of course, you are Catherine o'Flynn. 'What was Lost' begins with a child's story and tells it with clarity and sincerity. It's a gorgeous opening as is the novel that follows. Accomplished, heartbreaking and haunting: it proves that writing as a child can be simple, succinct and extremely succesful.