For booster vaccination, CDC recommends eligible people 6 months and older receive an age-appropriate, updated Pfizer or Moderna vaccine that offers better protection against variants, and the dosage and vaccine does vary.
The recommended vaccination schedule from the Centers for Disease Control and Prevention, including dosage, is available here. For more information about the safety, efficacy, and timing of each pediatric vaccine, please visit CDC’s page about COVID-19 Vaccines for Children and Teens.