Baby teeth. Usually a permanent tooth will erupt shortly after a baby tooth is lost, however this is not always the case. If a baby tooth is lost early due to trauma or decay then there can be delay in the eruption of the permanent tooth. If the permanent tooth is too crowded or in a bad position it may not erupt. A dentist an let you know if your child's teeth are erupting normally.
Different ages. Your milk teeth, or primary (deciduous) teeth are lost at different ages and stages. In most cases, the primary tooth will have a developing permanent tooth beneath it, which will hopefully replace it. There are some instances where a person may not have a permanent tooth to take the place of the primary tooth, and the primary tooth is not lost until later in life or not lost at all.