One family of kids (2 boys at 10 and 9, 2 girls at 4 and 6 months).

Initially the boys peed all over the area of the toilet and probably got some in it by accident.

What cured it, was them being forced to clean it up themselves. Cleaned up very well, not just a little bit, but with vigor.

Shortly after that they also learned to pay attention to the seat being up or down... due to having to clean it.

What burns me about "adult men" is that many places do not have auto-flush urinal or toilets. They just leave their shit and piss for all to see.