Generally you want to bring something that represents where you are from. Maybe bring a small gift for each member of the family, and one gift for the family as a whole. Nothing extremely expensive is necessary.
They will also return the favor and if you give very expensive gifts it puts the pinch on them to give
something of equal or slightly higher value.
Some ideas are: picture books or calendars, ashtrays, coasters, chocolates, fragrant bath salts
t-shirts or jackets of sports teams, BBQ sauces; dijon or dark mustards, unique salad dressings,
jams or other preserves, soap or shampoos, lotions, nuts, dates, dried fruits, flavored coffees and teas, keychains, postcards, mugs, and so on. Actually some cologne for one of the girls would be nice if it's a light fragrance that she likes. With oppressive school rules she can't wear it except on weekends and vacations, but that doesn't mean she wouldn't like it. You can bring in beef jerky too,
but you could run into some interference at Customs, so make sure the package spells out it is safe for export. Many makers even put a message in Japanese on the package.