preteen

/P R IY0 T IY1 N/
noun
  1. 1

    A child between 10 and 12 years of age, at the onset of adolescence.

adjective
  1. 1

    Of, relating to, or designed for, or being children between the ages of approximately 10 and 12.

Source: https://en.wiktionary.org/wiki/preteen