She acts as a kind of mini-director just for the child. "When the director wants a particular action from the baby, he needs someone skilled at getting that action on cue," she says. For a smile, a game of peekaboo just off camera is a winner. "Sometimes I pop up above an actor's shoulder to get the baby to look at the actor and then duck down to avoid the camera," says Adria. "You do need a good sense of camera angles and set." To get a baby to climb to its feet, she will dangle a puppet above its head. When an unhappy scenario is scripted, judicious pin-sticking is absolutely forbidden. "You don't do anything physical," says Adria sternly. "To get an unhappy baby, all you need do is turn your back and walk away. The baby knows it has lost your attention and will whimper. As soon as the scene is shot, you go and pick it up."
Adria makes sure her charges get regular breaks. "And we'd never use a baby if we were filming a fight or a scene with lots of yelling - the child would be filmed separately." In a Steven Seagal film she worked on, a small child discovers the massacred bodies of his parents in their bedroom. "We filmed him coming to the door, looking surprised," she recalls. "He was never on set with all the blood."
Adria, who is also a teacher and welfare worker for older children on set, is a veteran of Jurassic Park, ET, and several Indiana Jones movies, as well as commercials and TV shows. She prefers longer projects which allow her to establish a rapport with the actors and babies. The tight schedules of commercials means high pressure. "I leave those to the women from New York who have teams of assistants," she says. Given the limited time for commercial shoots, multiple back-up babies wait in the wings - for one Doritos ad, Adria had 40 to deal with. Girl and boy babies are interchangeable until the age of 10 or 11 months, she says. "You often end up using the second or third baby rather than the 'hero' baby, which is what we call the first choice."
Peter Robertson of Baby Wranglers Ltd is Britain's only such expert. "My job starts at pre-production," he says. "It's not just a question of being Mr Funny on set, you have to know about lighting and direction." And it is crucial, he says, to know a baby's own schedule - when it eats and sleeps: "If a child has to eat something for an ad, it won't if it's already full." For a grumpy reaction, waiting until the baby is tired usually produces the desired effect - or asking the baby's mother to take away a favourite toy for a moment. For a startled or alarmed expression, a loud noise does the trick, says Peter. "If they have to crawl they will often chase a ball rolled across the floor."
Peter is also something of a psychologist: "If a child isn't doing what it's supposed to, you have to find out why." He was once called in to rescue a shoot where the star would only run in circles. "They'd been filming for days and had nothing. The mother had been feeding the child sweets and tea with sugar in, so it was completely hyper." Sweets in general, he adds, are a complete no-no. "Bribery just doesn't work. After one sweet they want more and become upset if they don't get them."
Kamera Kids is a long-established childrens' agency. "We don't use children that are too clingy, too fractious, too sleepy, too awake, too anything," explains a spokesman. And the parents are crucial. "If the mother isn't happy, it makes for an unhappy child - we call it the umbilical effect." The agency says that beauty is actually less important than being photogenic - they were recently offered pounds 250,000 to find an ugly child to work in Hollywood.
Baby Wranglers Ltd: 0181 780 5234. Kamera Kids: 0181 675 4000.