My game never removes the childhood traits once they've expired, I have to remove them for myself using a cheat i.e. traits.remove_trait trait_ChildhoodPhase_Clingy but my teen is currently stuck with...
I just aged a kid up to a teen over the weekend and am so glad I did. He was ALWAYS tense b/c he didn't want to talk to anyone but mom and dad. It didn't bode well with his social butterfly trait/aspiration. :s :s