>But I never understood what people meant when they say a baby was born addicted to crack.

When we speak of addiction, there are two main types.

The psychological addiction or dependence refers to the mental and emotional state where someone feels like they need whatever it is to be normal. We can safely ignore this one in terms of babies, since they don't have well-developed minds to have those responses.

The physical addiction or dependence, however, refers to actual quantifiable changes in the state of the body that makes the body physically require the drug. Addiction to alcohol, for example, causes physical changes in the structure of the brain in order to adapt. Removing alcohol, especially suddenly, throws the body into disarray due to the sudden change in the chemical bath.

This is what is meant when doctors say a baby is "born addicted" to a drug -- their brains have already been changed in the same way as a drug addict's.