It depends upon the circumstances in which the parents and the child is. However, three years old child of our era seems able to enjoy the whole trip. A decade before it was good for children of 5 years old and two decades before children of 10 years age. The environment, knowledge, scinece and technology have brought a revolution through out the global village and children have become intgelligent ahead of their age. They are to shoulder responsibilites much more than us. Hence age factor seems to have changed.