A new photographic glimpse inside France's juvenile detention centres reveals a system where children as young as 13 are locked in cells for up to 23 hours a day, sleep fully dressed to protect their privacy, and count down days in notebooks that never seem to fill fast enough. The photographer found the cells "impersonal and intimate at the same time" - a window, cell bars, a rudimentary bed, a plank serving as a desk, and occasionally a book or some drawings. Once inside, "you quickly find yourself going in circles, with nowhere to go."

Due to staff shortages, young people may spend as much as 23 hours a day in their cells, a practice criticised by Europe's Committee for the Prevention of Torture, along with low levels of access to educational and sports activities. As one young detainee put it: "We're locked in our cells every day. Even though it can become our quiet corner, it's hard. Because of the way the buildings are laid out, the quiet corner is never really quiet. All the cells are connected to each other, and this is a place that invites outside intrusion. We are constantly being called out. The windows look on to the yard, and we hear screaming all day long. It's even worse at night."

For all prisoners, minors and adults, the prison yard is a mandatory one-hour stop each day. The cell windows overlook the yard, so it's almost impossible not to be watched. Every movement, every word takes place under the eye of fellow prisoners and guards. Detainees spoke of boredom and an altered, artificial sense of time. "I feel like being here is making me stupid. I feel like an idiot. I forget things. I've lost what I knew. I don't see anything new any more. In my cell, my vision gets blurry from staring at the same walls, especially on weekends, which feel like three whole weeks. I'm losing it here. TV drives me crazy, so I draw to keep myself occupied. It takes mental strength. Some people go crazy; they don't care about anything any more, as if they had nothing left to lose. I don't like being around the other kids, the ones from the other units. I'd rather go back to my cell to avoid trouble."

Out in the courtyard, one boy spoke of his love of nature - he wanted to photograph birds, sleep outdoors and wash in rivers. It was the day before his court hearing. He just wanted to talk, sharing everything crossing his mind: his mother and her drug addictions, his fear of the hearing, his lawyer, heroin, the desire to end it all, to stay here, to go elsewhere, the river.

In France, only three of the six juvenile detention centres are authorised to accommodate girls. They are housed in a separate unit but take part in the same activities and classes as the boys. In her cell, a girl described the paradox of feeling unsafe in a space entirely built around security and surveillance. "I'm always self-conscious when I'm in bed, afraid that someone might be watching me through the peephole. I no longer sleep in whatever position I want. Before, I didn't like wearing pants to sleep, but here, I sleep with all my clothes on. I don't know how else to protect my privacy. I don't show that I'm sad, so I hide my sadness. I don't talk about it with the other girls either, to protect myself. Girls are like that: the slightest argument, and the whole prison knows about it. Being a girl in detention isn't easy. When we scream, we really scream."

The disciplinary unit, where children are confined alone, was photographed while the cells were empty. Inside, there is a tiny concrete yard and almost completely bare cells, with no privacy. The windows are locked and cannot be opened. The narrow, grey yard exists only to allow the daily mandatory hour of outdoor exercise. On the walls, there are phrases written with faeces, as detainees are not allowed to have pens or personal belongings. For minors, confinement in the disciplinary unit can last up to five days, or seven days in cases involving violence. Under the law, children are meant to be given activities and occupied, but that is not always respected and can result in situations of de facto isolation. One young person described the experience: "I got a saw to cut through my bars, and because of that, I'm going back to confinement. In the hole, you're there, you stay there, that's it. You lose it - you just have to talk to the wall; there's nothing else to do. Honestly, some people want to kill themselves in there. It's too horrible. They call it the disciplinary unit, but you can't come out of there normal. It's not possible. You can't open the window. You can't turn the light on or off yourself. You have to call the guard to do it. They tell us it's a place to rest, but that's not true. You end up thinking about doing even worse things after going through all this."

One boy was found drawing lines in a notebook, crossing off the days, keeping track of time - a seemingly mundane act in prison. He didn't want to talk about it in his cell, but a few weeks later he spoke: "When I arrived, I took a notebook they gave me and drew lines to count the days I had left. I felt like doing it. And one day, I stopped. It wasn't making the days go by any faster. The hardest part is staying in the cell all day. The days pass more slowly than the nights. There's only a TV in the cell, and after a while I get tired of it, so I sleep. I try not to overthink things. I'd rather go see the social worker, as it gets me out of the cell and makes me feel better. I don't really care about meeting people, but the activities and classes help take my mind off things. If I get out, I want to continue my studies and find an employer for a work-study programme. It might be this summer, or maybe next summer. Trials can take a long time. I think you can go crazy in prison, but I'm not worried about myself."

The reason they are in prison is very often the same: drug trafficking. Outside in the garden, a boy stood among flowers the same colour as his sneakers and cap and quickly told his story. "I started at 10am, in a small park, with a shoulder bag. Inside, there was a really big package: 50 baggies, droppers and heroin. It was a lot of money. I had clients, and at one point I saw a BAC [Anti-Criminal police] team. I still had the bag on me when they grabbed me." The photographer noted feeling his account was embellished, or perhaps more glamorous than reality - recalling what an educator once told her about another young person who talked about his path in drug dealing. Knowing his judicial file, she told him, "But you weren't really in it." And he answered, "I know, I'm inventing a life for myself."

In the gym, a young person was playing football. He looked very young; his gaze was tired. He is an unaccompanied migrant. "I took an inflatable boat with 18 people on board. I arrived in Spain. Then in France 10 months ago, and I've been here for almost three months now. This is my first time in prison. I wanted to play football, so I came to Europe for that, and also for freedom. The stadium isn't far away, so I can hear the games from my prison cell. I love Lionel Messi, he's my model; he's the best player in history. I'm going to be a player."

In the shared space of the prison, another boy was having his hair cut. It was a special moment. The barber is well known on social media for the haircuts he gives in working-class neighbourhoods. His hairstyles are very different from those cut by the guards, which are often simpler and more uniform. The young people can choose the style they want. They trust him; he knows how to talk to them. One of the young people told of a 17-year-old friend of his who was murdered a few days after his release from prison - a settling of scores linked to drug trafficking. "The guys were on scooters. They pulled up next to him, pulled out a 'guitar' [a rifle], and shot him. He had a huge debt, and they took him out a few days after he got out. They did some crazy stuff to him - they kidnapped his older brother because he had changed the password to the Telegram account to keep his clients."

When a risk of suicide is identified, the young person is placed in a special cell called an emergency protection cell. Then a "single-use kit", made up of tearable clothing intended to prevent hanging, is given to them. While suicides here can be counted on one hand, there are more attempts. And then there are those who do not appear in any statistics, because they died some time after their release, outside the prison system. A member of the prison educational and medical team confided how difficult it is to face such situations. "It's the suicides that hurt me the most. One boy killed himself here, a week and a half before his release. It destroyed me. Another girl had been released and went to a specialised hospital unit, where she took her own life a few weeks later. We undergo training on 'identifying suicidal crises', but with little Jonathan, we never would have suspected it. To kill yourself just days before your release. These are moments we live through here, pains. But afterwards, what do we do with them? It's another death that will be forgotten."