Japanese are fond of soaking in the tub. In a Japanese bath, an extra-deep tub is filled to the top with very hot water, in which you sit submerged up to the neck.
Most people spend about half an hour in the bath every night.
Most children take their baths with their father or mother until they are in the upper grades of elementary school. The family tub is an important place for parent-child communication. One answer might be the climate. Japan's summers are hot and humid, and its witeres are cold. Hot baths wash the body's sweat off in the summer and warm the body up in the winter.