I've never seen anyone wash a childs' behind in a WDW fountain, but have seen plenty of kids putting their entire mouth on it. I've seen adults do stupid things too. On our most recent trip, we were in the Town Square Theater in MK. Frankly, I forget what we were waiting for, but we were sitting on the couches and saw they had one of those 5 gallon water coolers right near the restaurant, with little paper cups next to it. My kids wanted a drink, and before we got to it, and Indian lady walked up with her clearly used small plastic water bottle (like you'd buy in a convenience store). She put it right up to the nozzle. The CM nearby looked very panicked and was repeatedly saying "No, ma'am, you can't use that". The woman just looked at her pretending not to understand, even though the CM was clearly pointing and waiving her finger and head no. Poor CM was about to have a heart attack. I grabbed the water bottle and pulled it down and said to the woman "I think she's telling you no". The lady looked at me and just said "Oh, OK" and walked away. I just laughed and the CM then wouldn't let me use the cooler until she had cleaned it, but she seemed clearly relieved that I had made the lady go away.