Been reading up on these lately:

<< The first permanent molars usually erupt
between ages 6 and 7 years. For that reason, they
often are called the “six-year molars.” They are
among the “extra” permanent teeth in that they
don’t replace an existing primary tooth. These
important teeth sometimes are mistaken for primary
teeth. However, they are permanent and must
be cared for properly if they are to last throughout
the child’s lifetime. The six-year molars also help
determine the shape of the lower face and affect the
position and health of other permanent teeth. >>

http://www.ada.org/~/media/ADA/Publications/Files/patient_58.ashx

If your kids are older, do they have their 6 year molars yet?