A bartender who works at the Hot Bird in Clinton Hill told The New York Post too many parents were bringing small children to the bar.
"It became an issue. So we put up the sign," the bartender told the paper.
One angry mother posted about the ban on a parents' message board over the weekend, complaining she had been kicked out of the bar with her 15-month-old son, the Post said.
Bar customers supported the ban.
A 27-year-old bar-goer told the Post Tuesday night, "Kids shouldn't be running around where people are trying to drink and hook up."