As statewide eligibility for the COVID-19 vaccine expands to residents 16 and older, researchers at Stanford Medicine have set their sights on an even younger group: children ages 2 to 5.The medical school Wednesday began administering doses to children in the tender age group as part of a larger, three-phase trial of Pfizer-BioNech’s COVID-19 vaccine that will ultimately include children ages 6 months to 12 years.“We want to protect children just as we want to protect adults from this disease,” said Dr. Yvonne Maldonado, the pediatric infectious diseases expert leading the trial at Stanford. “The goal is to have a...