I am new to GMing (and role-playing in general, for that matter) and I am having a somewhat difficult time making plausible and interesting NPCs. This is especially true with NPCs who are not "typical adults", such as a child or an NPC who is unlike me. Most of the time, the interaction with the PCs turns into, "Ask me questions...uh...here is a quest...uh...boring stereotype...uh...".
So, what is the best way to make interacting with these kinds of NPCs both more realistic and engaging? Ideally, I want to turn NPCs from "I'm here for plot reasons" into engaging, memorable and realistic characters,