Paris attacks: Can Europe tackle homegrown jihad?
Their laughter ringing out around the sports hall, the group of youngsters, aged between 15 and 25, bounded about playing first football and then a burst of basketball.
You'd never guess by watching them the trouble some have been in with police, the misery at home others are experiencing or the fact that a few of them have no home to go to at all.
And that is the point.
The sporting rough and tumble was organized by Arktos - a guidance and training group in Leuven in Belgium that works with the socially vulnerable.
Their aim: to turn risk into opportunity, fear into openness, feelings of isolation into a sense of self-empowerment.
In Europe's fight against homegrown terror, prevention programmes like this are invaluable, reaching out to troubled youngsters before they gravitate towards radical ideologies.
"Police always stop us," 24-year-old Anouar Abdellati, a Moroccan-born Belgian, told me.
"People look at us like we are problem-makers from the Middle East. When I get on a bus it's like people kill with us with their eyes. I don't dare ask them anything - they'll think I'm carrying a bomb.
"I can't get a job, I can't rent a flat. People hear my name and hang up."
But Anouar is determinedly upbeat. He loves music and keeps himself busy making rap videos.
He genuinely seems to appreciate his sessions with Arktos.
"I can ask society to change, it will never change. People need to change because we have the power - not the society," he says.
"If a lot of people stand up like us, like the people you see here - we have the power. It's our responsibility to do something."
"That's why this project is really good. Because I have a lot of friends who don't come here and they are thinking in a really bad way. They start to hate cops. They start to hate white people. They start to hate."
And by that stage it's hard to reach out to those youngsters.
Europe has spent millions trying to de-radicalise extremists.
Homegrown jihadists played a crucial role in the bombings in Madrid in 2004, London in 2005 and now in the Paris attacks.
Last year, the European Commission launched the Radicalisation Awareness Network (RAN) made up of 700 experts and frontline practitioners from all over Europe.
I met one of the them, Moad El Boudaati, in the Central Mosque in Vilvoorde, a small town in Flanders with a Muslim population of 25% and a reputation for being a hive of radical extremists.
He told me that de-radicalisation was far from a straightforward process.
"What does it mean de-radicalisation?" he asked.
"Does it mean you put a youngster into a washing machine, after 10 minutes you put him out of the washing machine and then he's cleaned up?
"That you have a programme where, after 10 minutes, after 10 months, the youngster is de-radicalised? If you have that programme then tell me. But it's impossible. Each case of each youngster is different."
Moad has several acquaintances fighting in Syria.
He says better relations between mosques and social workers could help stop youngsters being lured towards extremism.
But he warns that all the talk now in Europe of forming a coalition to bomb Syria makes his job much harder and recruiting new jihadists in Europe far, far easier.
"They will say, 'You see they are still bombing your brothers and sisters in Syria and Iraq. Are they not humans? Are only the people in Paris humans and those who are in the Middle East animals?'
"It is very easy to talk in this way to youngsters and to recruit them. So we should be very aware of how we are actually managing our foreign policy, our foreign European policy in the Middle East.
"Instead of breaking society, maybe we should think about how we could build it? Not only using bombs but also using other possibilities. I think we should consider that."
Of course, it is one thing to become radicalised. Quite another to plot cross-border terror attacks like the Paris gunmen.
I asked the EU's counter-terrorism co-ordinator, Gilles de Kerchove, how Europe could be made safer for its citizens.
He warned first of all that prisons were not always the answer when it comes to dealing with extremists as they tend to act as a breeding ground for further radicalisation.
Better rehabilitation programmes are needed, he said, for those including Europeans returning from Syria "without blood on their hands".
But, he added: "For the people joining Daesh [another name for the so-called Islamic State group] as with soldiers who do military service together - it creates friendship, bondship, and that may be used later on.
"So if people get back [from fighting in Syria] more radical, better trained to use a Kalashnikov properly, make explosives in their mum's kitchen as one magazine has suggested - and with developed networks - it's a huge source of concern."
He said Europe had to become better at sharing information, at systematic controls on its external borders and at cracking down on the widespread availability of illegal firearms.
"We don't want to build a big brother society," he assured me. "But in some cases we do need more information, like passenger name records. There's an urgent need to use them to detect suspicious travel."
The attacks in Paris have left a lingering sense of unease all over Europe. Opinion polls indicate a willingness to lose personal freedoms just to feel safer.
It's a gut reaction to feeling vulnerable. But there is now a tension between having more police, more surveillance, more stop-and-search on the streets and preserving traditional European values like civil liberties and humanitarian ideals - like keeping the doors open to the world's most vulnerable.
So what kind of Europe do we want to be? What kind of Europe do we dare to be after Paris?
Bilal Benyaich is a senior fellow at the Itinera Institute where he co-ordinates research about migration and integration. He is also a policy adviser and author on Islamist extremism in Belgium.
"There is a big tension," he says.
"The migration crisis and the terror crisis that we have now in Europe. They are actually different discussions. We should not put them all into one basket.
"I think we should find our way between security and keeping a moral ground. We must take in refugees but we must ensure they are real refugees. We should keep our heads cool and be rational about these questions because what we are facing now, it is tough, but it can get a lot tougher."
And that - despite their resolute sounding statements - has Europe's leaders nervous. Really nervous.