After how many months can a baby start travelling with parents?

Honestly, right after the first day. Though it varies across cultures. Here in India, we have customs that prohibit the baby from going out till 6 weeks after birth. Mostly, the idea is to limit the kid's exposure to germs. However, in the western countries, mothers usually take their babies along with them even in the first week -- either for a stroll (to refresh both the mother's and the baby's mood), or for running the errands (when they don't have help). So, it depends on your family's priorities. Nevertheless, traveling with a baby is the easiest when they're super young. You don't have to worry about much -- they usually sleep for long hours and if they're not and you're breastfeeding, food is always available :)