In infants, colds progress through three stages. Here's a breakdown: After a baby is infected, there is an initial 24 to 72 hour period, characterized by fussiness and (often) mild fever, with generally clearer mucus. Following that is full onset of the condition, which lasts several days. At this point there may be fever breaks, the mucus turning yellow or green, and sneezing or coughing, among other symptoms. Generally, there’s a final few days when the baby has more energy, but some aspects of the infection linger.