Your baby’s first teeth usually begin to erupt through the gums at about six months of age, although the timing will vary among children. All of the 20 primary teeth should come in between the ages of six months and three years. Your child will lose his or her primary teeth between the ages of six and eleven. Your child’s first permanent teeth usually erupt behind the primary teeth at about age six. The last permanent teeth usually erupt between the ages of 12 and 21.