"excuse me, but there's a toilet inside"
The dad in question had just yanked the pants of his (estimated) four-year-old DS down outside the shop and instructed him to "piss up the wall". The little boy looked a bit confused and frankly embarrassed to be doing this. I (politely) called over to the dad and said the above. He told me "he's just a fucking kid" and told the boy to carry on.
Was I wrong to say anything? The child did not hear what I said, as the dad was standing at least 10-15 feet away and I made sure I said it quietly so as not to embarrass the child further. All parents get caught with a desperate child every now and then (I've been there myself!), but I fail to see how this dad could not have walked the child inside and led him to a cubicle. I really don't think I was wrong, the toilet was about a 20 second walk away and the child certainly didn't look like he wanted to pee up a wall. 