At my gym there are a lot of family programs on Saturdays, so there are a million kids around.
Last Saturday a kid (4yo boy) was racing around one of the main common areas where there is lots of traffic, and I heard his father say, in a very kind and friendly tone:
"You're not the only one in here buddy, you need to watch where you are going."
And the little boy slowed to a walking pace.
Nice to see good parenting in action.