What do you do when your LO starts flushing the wrong thing in the toilet? Other than following them to the bathroom each time, what can I do?

Try to keep things out of the bathroom such as towels, sanitary products, anything at all. If the person is mentally incompetent I have known them to flush their own glasses and dentures down, so it is seriously a problem. You might need to lock bathroom and keep a commode chair handy.

Thank you all for your answers!

You should begin using a portable potty this way you don't end up with overflows and accidents. My lo actually flushed or attempted diaper flushing and destroyed the bathroom and had to replace toilet.

Commode instead, or maybe one of those "hat" inserts they use in toilets in hospitals?

You have pretty much figured it out. DH aunt flushed so much paper I finally bought a toilet that claimed to be able to flush golf balls. It beat paying the plumber on a regular basis.

Unhook the chain in the tank so she can't flush. Simpler is turning off the water, but don't forget there will still be enough water in the tank for another flush unless you make sure to empty it.