Both pullet and cockerel chicks are usually transported within 24 hours of hatching to a broiler farm, like this one. What that means, then, is that when a new batch of day-old chicks arrives on William and Janet's farm, they were all hatched on the same day at the same place. At this age, the chicks are very tiny and could easily fit in your hand.
At the broiler farm, the young birds are carefully watched during this early stage, called the brooding stage. Brooding chicks must be kept very warm and the temperature in the barn is set at about 30 degrees Celsius for the first three days.