I have never heard of this expression before but I'm guess it refers to the fact that nowadays trains use digital signals instead and as a result they don't have caboose/brake van anymore. So (without context), it probably means that the person who said it believed that caboose is important and safer than digital signals? Or the trains will be safer to have a live human being watch out for it ?
Definition of baby. plural. babies. 1a (1) : an extremely young child; especially : infant (2) : an extremely young animalb : the youngest of a group He is the baby of the family.
baby noun [C]. A1 a very âyoung âchild, âespecially one that has not âyet âbegun to âwalk or âtalk: a ânewborn baby a six-week-old baby a baby âboy baby âclothes baby âfood Sandra had a baby (= gave âbirth to it) on 29 May. Owen is the baby (= the âyoungest âperson) of the âfamily. A2 a very âyoung âanimal: a baby âelephant/âmonkey âº disapproving an âadult or âespecially an âolder âchild who is âcrying or âbehaving like a âchild: It didn't âhurt that much-don't be such a baby!