IS this just par for the course? Have I been remarkably lucky not to stumble across women teaching their children to piss into sinks in public washrooms before now? Is this what you all do when Junior needs to relieve himself?
No, not at all. NEVER and NO. It is one thing to be accidentally body-fluid-ed by your own child (and still gross, just a fact of life, but one of the gross ones). To be confronted with a stranger having her child relieve himself in the sink of anywhere, but particularly in public facilities is not par for the course, at all. And you said she left behind soiled wipes, etc. too, correct? I was disgusted.
In fact, if my only place my child could relieve himself at the cinema were to be a sink, I'd probably take him outside and have him hide behind a tree and pee, because people will be using that sink to wash their hands, possibly the people who will pop my pop corn and get my soda.
Hec is right in that urine is (generally) sterile, but I don't freaking want it in my popcorn.