Especially if a grown man was talking to them about their restroom habits. I'm sure they'll appreciate the retroactive advice.

All snarkiness aside, if he feels the need to say something then I think he should probably address the parents. I certainly wouldn't have wanted an adult man say something to my little girls about anything regarding their restroom habits. I personally would just let it go. As stated in another comment, I got more than used to this in Brazil and I just don't think it's that big of a deal. Heck, with the amount of toilets I've had to unclog over the years maybe I should have adopted this method years ago.