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.
A small child is commonly referred to as a baby irrespective of his age though there are developmental stages in the first few years of the life of a human offspring. The smallest of babies are the newborns in the first few days of their lives. Infant is a word that is reserved for a kid before the age of 1 year. So, if you have a baby boy or girl who is a few months old, the doctor would refer to him or her as an infant. However, there are many grandmothers and grandfather who would take exception of this definition and call their grandchildren babies even when they are much older because of their extreme love for their grandkids.