The main reason to buy travel (medical) insurance is to cover the cost of medical care in the event of an illness or accident when your Japan trip.
While medical care is not particularly expensive in Japan (at least in comparison to places like the USA), medical costs can really add up in the event of a serious accident or illness.
In January 2017, one Thai woman collapsed suddenly in Ameya Yokocho in Ueno, Tokyo. Mr. Wanwisa Jae-jun (28) who came to Japan with a friend saying “I want to see snow.” Experts also had a severe heart disease with “survival rate less than 0.1%”. The one who saved the life happened to be a firefighter who happened to be, a doctor who carried out advanced surgery and treatment. Although Mr. Wanwisa who was saved miraculously, I had a treatment cost of over 18 million yen.
Nobody knows what happen for your and your kids.
If you don’t have medical insurance you better check https://tokiomarinenichido.jp/
Enjoy Your Japan trip!!