I entered the science fair as a kindergartner with a poster project explaining how (the output color-mixing of a) color TV worked.
Principal accused my parents of doing it; they had no idea what he was talking about and protested that I’d done it. So he interviewed me about it and left convinced I’d done it. ;)
When in doubt, a simple question like “why did you choose this topic?” or “what was the hardest part of this project?” will usually make clear the driving force behind the project. Some younger kids will just blatantly admit that their parents did the project (sometimes/often to the child’s dismay).
I had an english teacher in college accuse me of cheating. Well accused me in a roundabout way. My paper was on psychosurgery, and violent criminals. He said he needed to ask his girfriend, who had MFCC, how to pronounce amygdala. From then on I dumbed down my papers for him. I would purposely use a bunch of semicolons, and dashes.
I loved to write until I had that guy as a teacher.