What is the time frame for full growth of a six-year-old's teeth?

Varies: In addition to the terrific information you can get on the www.Ada.Org website, please understand that the ages listed are only averages, and that many children can take longer or shorter periods of time for their full dentition to erupt.

Within twelve months: I am assuming you are referring to just the eruption of the incisors (front four upper and lower teeth) or the first permanent molars which commonly erupt between the ages of 5-7. Once an incisor or molar has started growing through the gum, visibly full eruption should occur within a year (although it continues to grow imperceptibly for many years). If the tooth seems to be "stuck" seek consult.