Interview: Claire Keegan - 'A child's senses are not dulled by experience'

"Well I was, but I had no books," explains Claire Keegan in answer to my question as to whether she was an avid reader as a child. "And who knows, maybe that was a good thing because it put a longing on me for books. It really did."

The author of two short story collections – Antarctic and Walk the Blue Fields – and a new "long short story", Foster, Keegan is an exceptional writer. Her work is sparse and yet packed with emotional power; it resonates like poetry and is disarming in its intensity, a characteristic that describes Keegan in person too. In conversation, Keegan is considered, the pauses between questions and answers are cavernous, the precision of her language – perhaps the defining feature of her prose – apparent as she picks through questions and constructs her answers.

The youngest of a large Catholic family, Keegan grew up in Wicklow. Since there were no books in the house, apart from "the odd Mills & Boon floating in" and the library at her high school was perversely kept behind glass and therefore out of reach, her memories of the few books she could get her hands on are vivid.

"There was a travelling library but it came into the town and the town was miles away from us," she says. "I remember getting a book one time on hens, all the different types and breeds of poultry and ducks. I memorised them and had pictures of all of them in my head. But then I couldn't get it back to the library and they sent us a notice and it was something like 2 overdue fees, which was a lot on top of posting it back, so that was the end of the travelling library."

The only other book in the Keegan household was the Bible, kept in a sideboard in the parlour. It had coloured plates with paintings in between the text.

"I'll always remember one painting of a jaded-looking older man with Jesus and he was teaching a younger man, a teenager, how to press the crown of thorns down on to Jesus's head to get it on tight. I thought that was a marvellous and frightening picture. I loved how jaded the old man was, he'd done it so many times before. That was the first, and the most, adult book I've ever come across, if you like. It is about the awful things that we do to each other."

Foster is the story of a girl of about ten (her age, like her name, remains unknown) over one summer. Sent from home, where her mother is heavily pregnant and the family is struggling financially, the girl is to stay with John and Edna Kinsella, a couple whom she's never met. Suddenly the girl gets a glimpse of a different kind of family life and Keegan confronts her reader with the harsh realities of what it is to be a child. She brilliantly captures the girl's lack of agency: "I am in a spot where I can neither be what I always am nor turn into what I could be."

"I like imagining being a child," Keegan says. "And I've minded children for years. I used to mind children when I was little more than a child myself. I'm really interested in how powerless children are and how much at the mercy of their parents and their minders they are. And how they don't usually have anyone to go to if things are bad. I am interested in power, in how we treat and mistreat each other within our relationships and particularly in the relationships between parents and children."

The girl in Foster is dropped off with no bags, or clothes, no favourite toy. No-one asks her if she wants to go, or if she wants to stay. The tragedy is that almost instantly she knows that her temporary home is good.

As ever with Keegan, God is in the details. The girl watches a table being laid with food: bread, tomatoes, cheese and a jar of beetroot with a serving fork. Her father ignores the fork and "pitches it on to the plate with his own". It speaks volumes about the difference between her father and Kinsella. The girl sees it and she knows it. She knows, too, that the kitchen smells of freshly baked rhubarb tart, but also that it smells of disinfectant – it's a clean house, cared for. Perhaps if she stays there she will be cared for too.

"Surely, a child's senses are just as sharp as an adult's," says Keegan, "and maybe more so because they're not so dulled by experience. And disappointment. I think it's our own forgetfulness and frailty and weakness that we think the child isn't picking everything up."

There's a long pause before she continues. "There's a boy I know and he's fond of me and he comes over whenever I'm (at home]. And when I take him back in the evenings his mother always asks me, 'Was he bothering you?' And I think it's a painful thing to say to me in front of the child. She should ask me 'Was he behaving himself? I hope he was behaving himself? The difference between the two questions is the difference between sensitivity and insensitivity."

Keegan left Wicklow to go to Loyola University in New Orleans when she was 17. She arrived back in Ireland six years later with a degree in English literature and political science and set about trying to find a job. "I applied for 300 jobs and got 300 rejection letters," she says. Ireland at the time had the highest unemployment rate in Europe and a depressed economy. Keegan describes the period as "despairing" but there was a saving grace. She had a library ticket and she read "one good book every week".

"I also started reading Irish literature, which I had been avoiding. When I went away I wanted to get away from what was Irish. When I came back I wanted to see what Irish people were writing at that time, living writers. But I didn't at that time have any notion of writing myself. I didn't see myself as a writer. Still don't to some extent. I write but I'm more interested in writing than being a writer."

Writing for Keegan, who lives in the countryside in Ireland, happens in the morning. It's hard work, it demands concentration, quietness and intensity and that's exactly what Keegan enjoys. "Mostly it feels difficult and especially at the start it feels impossible," she says. "It does get easier once it turns into work, once you find a voice and some kind of situation and condition and you begin to feel the limitations of the story and the perspective coming into place. And then to try and carefully find the exact language for a situation and to imagine that life, which is a slow process."

The filtering down process for Keegan happens, she says, sentence by sentence. "That's the only way I know how to do it: by just trying one word over another. To some extent it's a matter of elimination, trying on different things which don't work until you come to something which is probably fairly simple which does."

Before doing a masters in creative writing at Cardiff University ("one of the best years of my life"), Keegan had admired the short story, especially the American short story, works by Sherwood Anderson, Carver, Cheever, O'Conner and Borges. For her own part, the length of her stories are decided, she says, by the work itself.

"There are certain demands each story makes on its author and I think the author either listens or doesn't listen and subsequently pays for it or is rewarded for it," she says. Keegan knew that Foster would cover one summer. It's a length of time that she felt meant it was not a short story but a long short story. "And I also knew that it would not be a novel unless I went into the two families. But I didn't want to go into the two families any more than I did. I felt that that was the right length. It would be too long if it was longer and too short if it was shorter."

For a moment I wonder if she's deadpanning. But she's not. "Yes, it would. I feel that that is a mistake that's made – stories are turned into novels. I would say most books are too long."

Foster is just short of 90 pages. Not too long, but entirely satisfying. Keegan is right: it feels exactly the right length. She says: "There's a wonderful Philip Larkin quotation when he says, 'Why did he think adding was increase? / To me it was dilution.' I love that. I do think that the more that's added, the less clearly we see. If we want to see deeply then we've got to see through less. We've got to discover what is essential to us to understand it more deeply."

• Foster is published by Faber, priced 6.99