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.
Infant - various definitions. Toddler - older. Explanation: In medicine, an infant is a child under 12 months (at least in the UK). However, in UK schools, the 'infant years' are (or used to be - the system is different now from when I was at school!) the period from ages 4 to 7. The child would then progress to junior school (often within the same school) at age 7. 'Toddler', as far as I know, has no definition in medicine and is colloquially used of a child who is big enough to walk but is still considered a baby - 'toddling' is the kind of unsteady walking associated with young children.