 The purpose of the study is to evaluate the immunogenicity and safety of Kinrix when co-administered with varicella Varivax varicella virus vaccine live, Merck and Company and measles mumps rubella MMR vaccines, compared to Kinrix co-administered with MMR vaccine alone. Both Kinrix and the second dose of Varivax are indicated in children 4-6 years of age, and there is great potential for the vaccines to be given concurrently. The aim of this trial is to demonstrate that co-administered Varivax does not negatively affect the immunogenicity or reactogenicity of Kinrix. 