Babies under the age of two must travel on the flight in the same seat as one of their parents. Therefore, they do not have the right to have their own carry-on bag. However, it is allowed to check in two more objects for free, such as the trolley or the crib. You have all the information in: «Hand luggage at Vueling: liquids, measurements and maximum weight«.
You have all the information in: "Hand luggage at Vueling: liquids, measurements and maximum weight".