Benny Chan described the filming process as some of the darkest days of his career, explaining that the baby was a factor beyond his control, and could not work more than eight hours a day. Whenever a scene involving the baby was shot, the crew members had to be silent, communicating in sign language. Benny Chan stated it took time, patience, and money to guide the baby through each shot, and numerous retakes were required due to the baby's constant crying and napping. As a result, production went over budget. Special methods were sometimes used to coax the baby into co-operation. One scene required the baby to suckle Chan's nipple. The baby was initially hesitant, but relented after the crew brushed a large amount of honey onto the nipple.
Although Louis Koo co-starred with Jackie Chan, a number of action scenes involving his character were shot with a stunt double. In addition, Koo was the baby's favorite on set whenever the baby cried, Koo was always the first to cheer him up.
Jackie Chan had originally intended to co-star with both Biao Yuen and Sammo Kam-Bo Hung, reuniting the trio for the first time since 1988 film Dragons Forever. However, Hung declined due to a scheduling conflicts.
Over 100 auditions were held before the suitable baby was found to star in the film. Benny Chan chose Matthew Medvedev, a one-year-old infant of Chinese and Colombian descent. Medvedev, known as Baby Matthew, was literally recruited off the street when an assistant director spotted him with his parents on the MTR. Although his family was simply visiting Hong Kong, they agreed to stay and let Matthew appear in Robin-B-Hood (2006).
Jackie Chan suffered minor injuries attempting stunts in the film, having been kicked in the chest by a stuntman wearing the wrong boots and fallen off a quad bike, while attempting to perform a wheelie.