A Japanese language class

Today I went to the city hall to have a Japanese language class for foreign residents. It was the first class for this year, because the only two students I teach were absent last week and the week before last. One of the students is Bryan, a guy from New York,USA, and the other is Emmet from Ireland. Emmet was absent today, too. Today,Bryan took one of his three sons,who was 6 years old. Bryan's son will enter elementary school in March, but he is very smart and can speak Japanese almost perfectly. I think it is natural because his mother is a Japanese. But what is not natural is that his father, Bryan, speaks only a little Japanese. He teaches English here at several parts of the city, and,at home,he communicates with his wife almost only in English. So, today, while Bryan was practicing Japanese, his son, sitting beside his father, understood almost all that I spoke. I always tell Bryan to try to speak in Japanese at home. On the other hand,for his children, it migtht be good that their father speaks only English, because they will become bilinguals.