It refers to someone, most likely a nurse or doctor, who has to deal with the care of those types of babies. Some addicts become pregnant, and since they are drug-addicted, it follows that their babies, when eventually born, are drug-addicted too! So, someone in a health-related field "works" with those babies just as we could say that they "work" with injured people, elderly people, etc. I hope that this helps you. J.