In other words "Please keep your children from running amok, bothering other customers, and generally being a real pain in the ass. They can act-a-fool, they just can't do it here".
Shockoe Coffee in VA. My new favorite-ist place. Any coffee house that can tell its customers to, you know, supervise their own children? And do so with with subtle, witty sarcasm?...well...that's just tits.