Whenever we go on a long trip (e.g. flight to Oz), my son always takes his Trunki, and loves it. Now he is too big to ride on it, and is a bit sad about giving it to his little brother, so I wanted to get him a cool new backpack or wheelie bag that he can use on the flight. Any suggestions? What is everyone's experience with a 5 year old and a wheelie onflight bag - will I end up carrying it?