Synonyms for Preteen (same or very similar meaning)
WordNet sense 1 (a preadolescent boy or girl (usually between 9 and 12 years of age)):
preteenagerWordNet sense 2 (of or relating to or designed for children between the ages of 9 and 12):
preadolescentWordNet sense 3 ((used of living things especially persons) in an early period of life or development or growth):
immature, youngFrom the ODE community, based on WordNetadd/edit