OP has at least one dog, so not a stranger, and no visitors, or the dog would have gone off, I think, waking OP.
The damage itself leads me to suspect age 11 thinking it is funny, or trying to prank the 6 year old who is scared of poltergeists by creating one, maybe after scary bedtime stories when they were alone. However, the plot seems a little complex for one 11 year old acting alone. What if the teens decided to prank the youngest with a faux poltergeist, and, clever little devils, decided to make the damage of a kind that points to the 11 year old? A sister could come up with that, and her cousins would egg her on and join in the fun. They are all good suspects, so I think handling it the way you did -- notifying the parents, not assigning blame, and imposing equal consequences -- was both correct and courteous. Especially since there are other, less likely but possible, causes, like sleepwalking or even mental illness, the parents might want to look out for.