The character needs strengths AND weaknesses; it shouldn't be perfect in everything.
The easiest way to start is to pick a personality profile - base it on a real or fictional character, an astrological sign, or whatever.
First are topics many adults can't handle without flipping out (politics, religion, abortion, gun control, sex).
Second are topics the child will have no interest or experience with (e.g., credit cards, alternative medicine, altruism).
Is it a stand-alone effort or is it going to contribute toward a greater whole?