According to IRCTC Train Booking, if you are travelling with your infant who is less than 5 years of age, he/she does not require a ticket for the journey. Children falling under the age of 5-12 years are charged fully if a separate berth/seat is taken for the child. However, if a berth/seat is not required for a child (5-12 years), then half of the adult fare is to be paid. Here full seats can be provided if a user pays full adult fare for infants or children.