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.
For other uses, see Baby (disambiguation) and Newborn (disambiguation). An infant (from the Latin word infans, meaning unable to speak or speechless) is the more formal or specialised synonym for baby, the very young offspring of a human or other animal. A newborn is, in colloquial use, an infant who is only hours, days, or up to a few weeks old.