Cries and laughter, clapping and calls and screams of delight fill the gallery. There are children everywhere on the multiple screens that fill the lower floor. Kids in Cuba careen round the streets of Havana on precarious trolleys fashioned from bits of wood and discarded junk. They rattle and slew on cobbles and jink round corners, under the amused and indulgent eyes of adults as they come hurtling past. The game is both exhilarating and frightening to watch, the young pilots and passengers inches away from hideous injury. Talk about health and safety. Little girls on a London housing estate swipe at each other’s conkers in a game that’s been largely banished from British school playgrounds. Of course, there’s a lot more to the culture of conkers than whacking horse chestnuts on a bit of string. How careful you have to be – preparing the conker, drilling it and threading it on to a string. All games, like art, have their rules and conditions. A young girl crosses the thronging streets of Hong Kong, avoiding cracks in the pavement, the boundary lines of pedestrian crossings, kerbs and tram tracks. Snaking between the traffic and careful where she steps, she’s on the move in a private universe. Children play rock, paper, scissors in Mexico City and hopscotch in a refugee camp in Iraq. A boy whisks old tyres along a broken road with a stick in Bamiyan, Afghanistan, shepherding the tyre and keeping it upright in his game with gravity. Another boy flies a kite under an endlessly blue sky in Balkh in 2011, an activity previously banned by the Taliban. There are games here that might have been played for centuries and games shaped by the present. Games adapted to a time and place and games that seem immemorial. Games of dare, dangerous games and games devised from contingency that foster collectivity and collaboration. Ingenuity, dexterity, risk, sheer pleasure and fun all play their part. The solitary and the collective all have their place. Play is vital, a way of being in the world. Both rooted in the real and symbolic, all creativity has its roots in play. In one way or another, it is at the heart of the work of Belgian artist Francis Alÿs, for whom the words play and work might well be interchangeable. One of his earliest works was to slide an ever-diminishing block of ice round the streets of Mexico City until it melted. Another time he wandered the streets carrying a handgun. He has stuck his head into tornadoes and persuaded a large group of people to move a hill with shovels. He once let a fox run free in London’s National Portrait Gallery and filmed its nocturnal wanderings with the gallery’s surveillance cameras. The Antwerp-born artist, who first trained as an architect and moved to Mexico in 1986, has been filming children’s games for a quarter of a century. There are now more than 40 films, the latest being shot in the area around the Barbican, in collaboration with local schools. A boy makes repetitive, cursive marks on the tarmac with a big lump of chalk, the gravelly sound as mesmerising as the lines proliferating beneath his hand. One of the ways Alÿs gets to know a place is by walking and watching, and seeing how children play in different places. He has filmed kids skipping stones over the waves in Tangier and racing snails, their shells daubed with brightly coloured paint, in Belgium. In Mosul, in Iraq, in 2017 he filmed adolescents playing football on a street devastated by bombing. Surrounded by burnt-out cars and shattered buildings, the two teams run and tackle, slide and dribble and head a ball that isn’t there. There never was a ball in this balletic interplay of perfect headers and invisible goals, dancing feints and effervescent team spirit. Play ends when distant gunfire echoes in the evening. A caption tells us that when the jihadist group Islamic State controlled the city in 2015, 13 teenage boys were publicly executed for watching a soccer match between Iraq and Jordan on TV. In a normal suburb wrecked by war, a car drives through Kharkiv in early spring. A group of three boys in military camo gear, shouldering defunct rifles, flag down the passing traffic, asking to see passports, and sometimes checking car boots. What’s the password, the boys ask? “Palyanitsya” comes the reply, a Ukrainian word for bread that Russians find hard to pronounce. Some traffic rattles by but many stop, indulgently. How much of this is a game? Later, on a single screen in the upper galleries, children mimic the awful cadences of air raid sirens. At the current Venice Biennale, the Ukrainian Open Group, showing in the Polish pavilion, asked Ukrainian adults to imitate the sounds of rockets and sirens and explosions, the whumphs and blasts and whines of bombardment. In Alÿs’s Siren the sound, part of a game played by Ukrainian children called Air Raid Alert, becomes an intolerable keening for one child performer, who suddenly flees the camera. Everything here is a collaboration with the participants. Alÿs knows when to stop. A number of black and white, hand-drawn animations are projected on the black-painted walls of the upper galleries. In these silent vignettes, fingers walk, legs swing back and forth (as though their owners were sat on a bench or a branch, idly swinging their legs), thumbs wrestle and many hands slap on top of one another. Other hands make the shadowplay shapes of rabbits and ducks. A couple of the bays in the upper galleries can also be used to cast your own shadows or to negotiate the space on little wheeled stools. And throughout the show Alÿs’s small, spotlit paintings punctuate the journey between the screens and the aural and visual cacophony. So delicate are the artist’s little paintings – wind in the trees on a corner in Vicacruz, a cyclist on the Malecón in Havana, ordinary life going on amid terrible wreckage in desperate places, you’d think they might disintegrate just from being looked at. Dozens of children’s eyes, like a shoal of fish, float against a gold-leaf background. They’re looking at us, as we are looking at them. However riotous it is, Alÿs’s Ricochets is an often heart-stopping and frequently beautiful show, and the archive of the Children’s Games – far more than are shown at the Barbican – is freely available to view online. What a gift.