It is possible and, in fact quite common, for cafe au lait birthmarks to change or grow as a person ages.
More Info: Many children are born with a cafe au lait birthmark. This type of birthmark is characterized as a darker area of skin pigmentation. While there is no known cause for this birthmark, it is thought to be an increase in melanin that is deposited in certain areas of the skin. While most children are born with one or more cafe au lait birthmarks, they may also develop and become apparent within the child's first year. This darker skin pigment is more common in those with deeper skin tones, such as those of African-American or Native American descent.
Cafe au lait birthmarks are harmless. They are not painful. However, for children that have more than a few of these birthmarks, or their cafe au lait birthmarks appear in an unusual size or quantity, they should be tested for other conditions and diseases. For example, neurofibromatosis is closely related to an increased rate of cafe au lait birthmarks. This genetic disorder affects the nervous system.
Unlike other skin conditions, a changing or growing cafe au lait birthmark is not necessarily anything to be worried about. Of course, you may still want to be tested for things like cancer or other complications if you notice a distinct and sudden growth of these birthmarks, on either yourself or your child.