My son used to drop his milk bottle into my QT tank. I also used to find little small plastic animals (giraffe, tiger, etc) in the PVC fittings. They were probably in there for some time before I discover.
The bottle always comes out right away. At least when I'm home.
No negative outcomes. Tank is still going strong with a pair of happy clowns.
Just recently my son distracted me as I was dosing my 2 part. I ended up adding the amount of Cal but it was actually Alk causing my Alk to jump from 8 to 14 DKH in a matter of minutes. I lost a lot of SPS since then and the tank is starting to recover after many large water changes.
This weekend my 2 year old emptied a pack of baby wipes into my sump, my skimmer went crazy, it dose not seem to have any negative affects on corals and fish.
And one day before my 5 year old clames that one of his toys feel in to the tank so he tried to get it out with the long tank tweezers that I have, and of course he nocks off some corals on the way.
My wife and I went away for the weekend and my twenty year old threw a frat party in the house. They cleaned up good but missed some of the evidence because I found an ace of hearts in the tank and two beer pong balls in the sump.