I tried your suggestion posted, and reset the mental/creativity back to 9. Sure enough, as long as I tried each adult skill after hitting level 10 of the corresponding childhood skill before saving (someone surmised this is when the glitch occurs), my child sim was able to earn the skill (charisma, violin, piano, pipe organ, logic, video gaming) like pre-glitch. An issue with that is the skill chart won't auto-populate the 10th skill again, looking like it is unfulfilled, but the trait is already there so it stays with them.
Another side glitch that resulted from this bug? My child sims don't register instrument playing for the creativity aspiration (play 5 hours). I haven't been able to test it yet with a child sim where I haven't had to reset the creative skill (since this glitch appeared), but my sims didn't show any hours played on any instrument at all toward the aspiration goal. I had to cheat the aspiration fulfilled which I hate doing.