So there's a workaround for this problem- once your child has maxed a childhood skill, be sure to have them get started on all the adult skills related to it, BEFORE you save the game. For example, they max out Creativity: right away, have them practice a bit on violin and piano, long enough that they pick up those skills. If you have a pipe organ available, practice that too. THEN it's ok to save the game.
Does anyone know all the adult skills a child is able to learn? I just had a kid max Creativity, so I had her play a little bit on the piano and violin, not too worried about pipe organ. Pretty sure that Creativity just gets you those 3 instruments?
Mental gets you Logic and Fishing, is there anything else?
Social gets Charisma... does it also do Comedy and Mischief?
And as far as I could ever tell, Motor doesn't unlock anything. Kids can't use workout equipment, or even jog, and they never seem to get Fitness when swimming.
Edit: Creativity also opens up Singing, just tried it.