I have to agree with turtle here. Whatever happened to discipline?
There is nothing wrong with your water heater, nothing wrong with your
The problem is your kids are inconsiderate, and that is what needs to
You could spend thousands on plumbing equipment to fix the problem, and
the kids will work a way around it.
If you are dead set on spending money to fix the problem - I'd hire a
plumber to cap the hot water feed to their shower. A week or 2 of cold
showers may provide the incintive you are looking for.