When a parent has two or more children on either side of them holding their hands, for the fear of losing them, creating a wall that can block people walking in a crowd.
Dave: "Hey Tom, i've been waiting in this hot dog stand forever! What took you so long?"
Tom: "sorry there was a sudden crowd that came to the bathroom after the 7th inning, and I was held up by tons of child chains."
Dave: "Kids and their small bladders."
Tom: "Ughh... I know."