Even with all the responsibilities and bad experiences I've as an adult, I wouldn't want to be a kid again. Being a kid was hard. People often don't care very much about your feelings or your personal comfort. You have very limited autonomy. You don't always know how or what you need to communicate in a given situation. The world is terrifying because you don't know how any of it really works. Adults might abuse their authority over you. Grade school is often an exercise in teaching you to unquestioningly accept authority.
That's my experience, anyway. Which is why, though I also have many good memories from that time, I wouldn't want to return to it. I remember being so incredibly excited to turn 18 because I could finally sign my own name on things without needing a parent or guardian signature.
